Saturday, December 10, 2011

Is there such a thing as totally safe food?

The short answer is "No!".  Even if we eat only sterilised food, such as canned meat, we are reliant on the proper delivery of the sterilisation process and prevention of post-process contamination.  Low acid canned foods are essentially sterile - the food is hermetically sealed in a can, which is then processed under pressure to destroy bacterial spores, specifically, the process is designed to reduce the chance of survival of a Clostridium botulinum spore to less than 1 in 10^12.  On that basis, you have a better chance of winning the PowerBall lottery than getting botulism.

But nobody wants to live exclusively on canned food.  Are there any other ways that we can make food safe, or at least reduce the risks of food poisoning to acceptable levels?

Yes!  Food microbiologists and food processors study the bacteria that can cause food poisoning - pH range for growth, water activity range for growth, requirement for oxygen, growth temperature range, response to preservatives etc. - and they also look at the intrinsic parameters of the food - pH, water activity - and then consider the storage conditions, such as relative humidity, temperature and atmosphere in the pack etc.

Taking all these factors into account, foods can be designed to be safe under proper conditions of handling and storage.  A significant part of the training of  food technologists centres around study of these conditions and manipulation of the conditions in the food to achieve the manufacture of safe foods.

As an example, look at a tank of raw milk on the farm.  Immediately after it is drawn from the cow, the milk is chilled.  This reduces the growth rate of bacteria, which come either from the cow or the equipment.  When the milk arrives at the processing factory, it is pasteurised - the temperature is raised to 72C and held for 15 seconds.  This kills all the vegetative pathogens, that is, the bacteria that are not in the spore form.  The milk is now safe, but will not keep indefinitely, because heat resistant spoilage bacteria are still present.  We can make the milk keep for a much longer time by ultra high temperature processing (UHT).  In this process, the milk is heated to around 140C and held for a few seconds.  This sterilises the milk, so there are no viable bacteria to cause food poisoning or spoilage.

The milk can be dried to powder.  This lowers its water activity below the threshold for bacterial or mould growth.  Alternatively, the milk can be fermented to yoghurt or cheese by addition of starter cultures.  The starters convert lactose to lactic acid and reduce the pH of the milk until it curdles and sets.  pH is a measure of the acidity of the food; the scale runs from 0 to 14.  Numbers below 7 are acid, those above are alkaline.  As the pH falls, fewer and fewer bacteria are able to grow.  Below pH 4.0 no pathogens are able to grow.  Typical pH of yoghurt is 3.65 to 4.40

Other foods may be made safer by the application of hurdle technology, where several preservation mechanisms are brought together to prevent growth of pathogens in the food.  There is a number of new technologies appearing, such as high pressure processing, electron beam irradiation and ohmic heating.  None of these processes can guarantee safe food, but each has its advantages.  I'll look at some of these techniques in future postings.

Safety management systems, like HACCP can be used to control food processing operations to ensure that safe food is produced.  However, some foods are inherently less safe, such as raw vegetable sprouts, raw shellfish, or very unusual foods that require highly skilled preparation, such as fugu.
Consumers must take some responsibility in their choice of food and eating habits.  If you are doing the traditional turkey for Christmas dinner, ensure that it is properly cooked - use a meat thermometer - and consider cooking the stuffing separately.

If you are going to barbecue this Christmas, don't cook chicken legs on the BBQ without first microwaving them - they are an irregular shape and ensuring that they are properly cooked is difficult.  Don't use the same plate or utensils for cooked meat as for raw.   Don't keep foods beyond their use-by date and ensure that all raw foods are refrigerated during storage. 

Have a wonderful holiday and keep safe this Christmas.

Friday, December 9, 2011

It's the pits - bacterial hideaways

Modern food processing is often carried out in stainless steel equipment - tanks, pipes, valves and conveyors are commonly made of various grades of stainless steel.  We tend to think of "stainless" as not suffering from corrosion.  To a large extent, this is true.  Stainless steel has a natural oxide coating that prevents water molecules from oxidising the iron.

However, stainless steel can still corrode where grain boundaries or embedded contaminants allow water to access the iron.  The contaminants might be grinding swarf from welding or repairs.  Stainless steels may therefore benefit from a process called passivation, in which the surface is cleaned with sodium hydroxide and then treated with nitric acid.  This restores the oxide film.

We use stainless steel in our laboratory experiments and routinely passivate with hot nitric acid.  One of my students used a bottle labelled "Concentrated nitric acid" from the chemistry laboratory to passivate some new samples.  Unfortunately, it appears that the contents were actually Aqua Regia, a mixture of nitric and hydrochloric acids.  (How often have I said that correct labelling is critical in food safety?).  

Chlorine ions are extremely electronegative and react strongly with certain compounds.  They can severely damage stainless steel.

The first photograph shows two coupons treated with the acid mixture.  It is obvious, even to the unaided eye, that the surface is pitted.  Chloride pitting tends to occur at right angles to the surface, so deep pits form rapidly.  Obviously, the use of aqua regia is a very extreme case of chloride attack, but even food materials containing sodium chloride will eventually attack stainless steel.  Even 316 stainless steel, which contains molybdenum that helps to stabilise the passive film, will corrode if exposed to high levels of chloride ion, or if the oxygen level is very low.  This is what may happen under a biofilm, where the bacteria use up the oxygen.  The area then becomes anodic and current flows, resulting in corrosion and the formation of a pit.

I took a couple of coupons to Dr. Jen Wilkinson who runs our Scanning Electron Microscope.  She took the following images, which show clearly the damage to the surface and the deep pits caused by the corrosion.  The second image below shows the interior of the pit.  Bacteria could easily enter the pit and would be very difficult to remove during cleaning.  If the bacteria form a biofilm, they will be protected by the extracellular polymeric substances (EPS) which glue them to the surface and may inactivate disinfectants.  The bacteria will be impossible to remove.

Wednesday, December 7, 2011

More on antibiotic use in animal rearing

I wrote last month, suggesting that it is high time we banned the sub-therapeutic use of antibiotics currently used in human therapy for animal rearing. 

When I wrote the article, I was not aware that the Food and Drug Administration had, around 9th November 2011, rejected two petitions to ban antibiotics from being used in food animal production. The petitions were filed by a coalition that included  the American Public Health Association and the Union of Concerned Scientists.

It is troubling that in its denial letter, the FDA acknowledged that its “experience with contested, formal withdrawal proceedings is that the process can consume extensive periods of time and agency resources.”  I interpret that to mean that FDA may well think that antibiotic use should be banned, but it can't afford to force the issue.

Meanwhile, researchers at McGill University have shown that bacteria resistant to tetracycline and tylosin can be isolated from pigs raised in a swine complex 2.5 years after administration of these antibiotics ceased.  See Microbial Ecology  DOI 10.1007/s00248-011-9954-0  published on-line 14th October 2011.  Antibiotic resistance genes were found in the bacteria, though the workers were not able to explain their persistence long after antibiotic use ceased.  The results are of significance for both animal and public health because these antibiotic resistant bacteria can be transferred between animals, humans and the environment.

Friday, December 2, 2011

Don't always blame the chicken - it spoils my sleep

"The human understanding when it has once adopted an opinion ... draws all things else to support and agree with it. And though there be a greater number and weight of instances to be found on the other side, yet these it either neglects or despises, or else by some distinction sets aside or rejects".   Francis Bacon, 1620.

A few years ago, I was flying from Hong Kong to Auckland.  I sat with two attractive young women and enjoyed a glass of champagne with them before dinner.  After the meal and film, the girls went off to spend time with other members of their party and I settled down for a sleep.

Some time during the flight, the cabin attendant shook me awake: "Dr. Brooks.  Are you a real doctor?".  Suppressing the urge to take him by the throat and educate him about academic qualifications, I asked what was the problem.  It seemed that one of the girls and two others of their party had been taken seriously ill, and the attendant wanted me to open the airliner's medical pack to use the rehydration fluids for the victims.  I explained that I was not qualified to do this and headed off to the galley to chat to the stewardess and persuade her I was really in need of a beer and some sandwiches.

Some time later, the girl who was not ill told me that her friends were vomitting and had diarrhoea.  "It was the chicken pizza we had in the lounge before we boarded".  The timing and symptoms didn't seem right to me and I asked a few questions, including what they had been doing in China.  "Oh, we've been at a furniture expo for the last week".  It didn't seem to occur to her that she had been snacking on canapes and eating buffet-style meals for the previous seven days; she immediately blamed the chicken.  When we landed, her friends were taken by ambulance to the hospital, suffering from severe dehydration. I never heard from them again, but my money is on the meals during the week, not the chicken.

Now whenever I fly international, I ensure that my ticket is booked in the name "Professor Brooks".  I'm more likely to get a decent sleep during the flight.

Your all-time favourites

I have just reviewed the most common search terms resulting in visits to this blog.

By far the most common has been "Coliforms in food".  This has been a regular search since I started writing Safe Food in 2006, but has perhaps appeared more frequently since the Escherichia coli O104:H4 outbreak in Europe.

Coliforms are used as "indicator organisms" to show whether the food has been processed under hygienic conditions.  Presence of these bacteria mean that the food has potentially been contaminated with faecal material and hence faecal organisms, but to confirm this, we look for Escherichia coli presence in the food.

Surprisingly, the next most common search has been "Safety of Probiotics".  Probiotic bacteria are those that confer some benefit on the host.  Thus many foods, such as yoghurt, contain live bacteria that may colonise the gut of the consumer and confer some benefit.  These bacteria are often lactic acid bacteria.  Many claims have been made for the benefits of consumption, though there are some indications that administration to critically ill patients with acute pancreatitis may have deleterious effects.  There is also some evidence that administration to infants under 6 months of age may render them more prone to development of sensitivity to allergens.  For the majority of consumers, however, probiotics will not be hazardous and may be beneficial.

Do not confuse probiotics with "prebiotics".   These were so named by Marcel Roberfroid in 1995, who later wrote the definition: "A prebiotic is a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health."  A major class of prebiotic is soluble fibre.

Much lower down the list are "Listeria in vegetables" and "Safety of chicken".  There has been a small spike in Listeria searches, probably as a result of recent recalls and the cantaloupe outbreak in USA that has killed approximately 29 people.  The incidence of listeriosis is very low and victims are usually neonates, the elderly and those people with compromised immune systems, but this outbreak seems to have been particularly dangerous.  Chicken has made regular appearances in the news, either being a vehicle for Salmonella or Campylobacter.  The incidence of Campylobacter infections in New Zealand has dropped significantly since the introduction of more stringent controls and biosecurity systems.

One new search now appearing is a bit disturbing: "Will eating spoiled food make you sick?".  I have previously written on this after receiving a direct question from a reader.  Is the increased interest a result of hardship in the community, or merely a thirst for knowledge?  I hope it is the latter.

Monday, November 14, 2011

Time to ban antibiotic use in animal husbandry?

As a microbiologist, I sometimes worry that we are killing the golden goose in terms of our ability to combat human disease.  As I wrote earlier, the cost of developing and bringing to market new drugs is astronomical and many companies are shunning new drug development in favour of more lucrative endeavours, such as development of molecular-based test kits for human disease diagnosis.

In this light, it is disturbing to read of the amount of antibiotics used in animal production.  In 2001, Kristin Leutwyler wrote in Scientific American that a study by the Union for Concerned
Scientists had shown meat producers in the USA feed around 25 million pounds of antibiotics to chickens, pigs and cows for non-therapeutic purposes each year (the antibiotics suppress microbial populations and lead to increased growth rates of the animals).  Compared with this, only 3 million pounds per year are used for treating human disease.

In 2009, the House Committee on Rules held a hearing: H.R. 1549 - Preservation of Antibiotics for Medical Treatment Act of 2009, which would have amended the Federal Food, Drug, and Cosmetic Act to require the Secretary of Health and Human Services to deny an application for a new animal drug that is a "critical antimicrobial animal drug" (CAAD) unless the applicant demonstrated a reasonable certainty of no harm to human health due to the development of antimicrobial resistance attributable to the non-therapeutic use of the drug.

The CAAD is a drug intended for use in food-producing animals that contains specified antibiotics, or other drugs used in humans to treat or prevent disease or infection caused by microorganisms. The Rule would also require the Secretary to withdraw approval of a non-therapeutic use of such drugs in food-producing animals two years after the date of enactment of the Act unless certain safety requirements are met.

That rule died in Committee.  It has been reintroduced in the 2011-2012 Congress, and went to Committee on 9th March, 2011. 

It has been argued that there are no good studies linking antibiotic use in animal rearing to the development of antibiotic-resistant diseases.

While this may be so, and I'm not sure that it is, it is hard to imagine how else multiple antibiotic resistant strains of bacteria could be found in animals and ultimately in humans.  A classic experiment shown to most undergraduate students of microbiology over the last 50 years is the selection of antibiotic-resistant bacteria.  All that is required is the production of a concentration gradient of antibiotic across a Petri dish.  The agar is seeded with the target bacteria and those that grow at the most concentrated side are picked off and recultured on another gradient.  Very quickly, a resistant strain can be isolated.

This laboratory procedure is effectively repeated in animals fed sub-therapeutic levels of antibiotics in their diet or drinking water - the survivors of the first dose are constantly exposed and eventually dominate the population.  As microorganisms transfer genetic information among themselves, the number of different strains resistant to the antibiotics also increases.

I would be less concerned if the antibiotics used for treating animals were no longer in use for human therapy.  Then the benefits could perhaps be justified, though even then, the class of antibiotic is important, as bacteria becoming resistant to one member of the class might also develop resistance to others.  If humans become infected by strains resistant to antibiotics used in human therapy, there may be no cure available for the infection.  These infections could easily be transferred by handling raw meats from treated animals, though there is again a lack of sound scientific evidence.

The view is clouded by the indiscriminate use of antibiotics by humans.  It's not just a case of doctors prescribing antibiotics when they are not justified, though I have seen antibiotics prescribed for viral diseases, which generally can't be treated with these chemicals.  Look up "availability of antibiotics over the counter" and you will get pages telling you that there is none.  However, it is well known that antibiotics can be bought freely over the counter in some countries.  Even the antibiotics of last resort - the only ones that can treat certain diseases - can be bought in pharmacies in some Asian countries and there are papers in the scientific literature showing the levels of resistance in bacterial populations.

I truly hope that President Obama eventually signs this legislation and that leaders of other countries do likewise.  I would hate for us to descend to the state before the introduction of penicillin, when even a scratch from a rose thorn could result in painful death.

Tuesday, November 8, 2011

Those dreadful scientists - do they ever do any good?

 If you read the popular press, you could be excused for thinking that scientists, particularly the genetic engineers, are a pretty bad bunch.  Wandering round spooky laboratories wearing white coats, these bearded boffins invented preservatives that are now widely used in processed foods, they developed milk pasteurisation and homogenisation, and the genetic engineers made corn with built-in insecticide.  Food technologists are employed by food manufacturers to make food keep forever and fool the consumers.

My perhaps somewhat biased view is that this is absolute rubbish.  To name just a few good things, we have safe food and effective vaccines, a whole range of new fruit cultivars and wonderful test kits that can quickly diagnose all kinds of disease.  All these things were developed by scientists, technologists and engineers.

A recent report from Cornell University describes a new test to trace and identify outbreaks of foodborne disease.  So far this is applied only to a common Salmonella subspecies, but the principle can be applied to many other foodborne disease bacteria.

One way of recognising a specific bacterial strain, such as one suspected of causing a food poisoning outbreak, is to chop up the DNA into bits with enzymes and to amplify the bits, followed by separation of the fragments by gel electrophoresis, which is a way of creating a band pattern or fingerprint.  Alternatively, parts of the DNA can be amplified with random primers, or starting sequences, that will also produce a fingerprint.  You will have seen DNA fingerprints used for crime detection in various television series.  However, it is never as quick and simple as portrayed in these cop shows.  Unfortunately, closely related bacteria may produce band patterns that can't be distinguished, making it impossible to differentiate one strain from another.

With the development of very rapid sequencing techniques, it is now possible to determine the nucleotide sequence of the full bacterial genome.  In other words, we can read the whole genetic code of the bacterium.  Very closely related strains may differ by only a few nucleotides, or code letters.  By looking at these very small differences, we can tell if a particular strain was responsible for apparently linked illnesses in Germany, United Kingdom, New York, and France.  The technique is called Single Nucleotide Polymorphism (SNP) test.

The technique is still quite expensive, but as rapid sequencing is developed further, the cost is likely to decrease.  Being able to track an infecting bacterium, such as the Escherichia coli that caused so much disease and death in Europe earlier this year, is a valuable tool in fighting such outbreaks.  In the face of such devastating outbreaks of foodborne disease, the cost of full sequencing is insignificant.

The researchers, led by Martin Wiedmann, who developed the technique intend to continue perfecting the method and to apply it to other bacteria.

Of course, the description above is a gross simplification of the SNP test.  Wiedmann's original paper is highly technical.  You can read it in:
Applied and Environmental Microbiology, 2011; DOI: 10.1128/AEM.06538-11

Alternatively, you can read a press release from Cornell University at:

Tuesday, October 11, 2011

Food Safe Families: Does it Prevent Contamination of Foods? Guest Editorial

Patricia Walling*

In just about any news medium, headlines about recalls of meat, poultry and produce due to contamination occur with deadly regularity. Sadly as anyone in health care knows these headlines aren't just hype; food borne diseases can be fatal. This is especially true when they infect the very young, elderly and those with compromised immune systems.

According to the Center for Disease Control and Prevention (CDC) “each year, 1 in 6 Americans, or 48 million people get sick, 128,000 are hospitalized and 3,000 die of food borne diseases.” The agency notes that among the 31 known food borne pathogens, the leading causes of deaths and hospitalization are: Salmonella, Toxoplasma, Listeria, norovirus and Campylobacter.

Based on this public health problem, a partnership was formed among several U.S. governmental agencies (including the U.S. Department of Agriculture, the Department of Health and Human Services, the Food Safety and Inspection Service, Food and Drug Administration and the CDC) that are charged with keeping the food sources safe in conjunction with the Ad Council. The campaign, recently announced by the USDA, is titled “Food Safe Families.”

These organizations feel that this promotional effort will “shift the way people think about food handling so they can take a more proactive approach at home to help reduce food-related illnesses.” However, not everyone feels this educational and health promotion campaign will do much to solve the real challenges of the food distribution system.

The Food Safe Families Program

Public service campaigns, created by U.S. governmental agencies have a storied history. From the iconic U.S. Forest Service and Ad Council campaign that featured Smokey Bear admonishing that: “Only you can prevent forest fires” (launched in 1947), to the FDA’s “Food Pyramid” (first launched in 1992, updated in 2005 and then replaced in 2011), there have been hundreds of public service campaigns that are well-meaning but often ineffective.

Will the Food Safe Families campaign have the promotional “legs” of Smokey Bear’s message or join “Just Say No” campaign as a waste of taxpayer money? Only time will tell. However, the campaign includes several aspects that make it important.

According to the USDA Food Blog, “using the motto “Check Your Steps,” Food Safe Families aims to get consumers to adopt four very easy steps when preparing food:

1. Clean: Clean kitchen surfaces, utensils and hands with soap and water when preparing food.
2. Separate: Separate raw meats from other foods by using different cutting boards.
3. Cook: Cook foods to the right temperature by using a food thermometer.
4. Chill: Chill raw and prepared foods promptly.”

These four steps – clean, separate, cook and chill – serve as the graphic and messaging platform of the campaign. The agencies hope that by constantly reiterating this message, it will become ingrained in those who are charged with preparing the family meals.

Even the timing of the launch was important. The agencies choose Jun. 28, 2011, because this is the start of summer and represents the prime outdoor grilling season for most families. The USDA noted in its blog that “food borne illnesses tend increase with more outdoor meals.”

Once the campaign was launched, it seemed that Food Safe Families had covered most of the promotional bases. There were spiffy new graphics, memorable message points, an innovative social media campaign and public service media all up and running. The timing and execution of the campaign was excellent, until people started showing up in emergency rooms with symptoms of Listeriosis.

The Listeria Outbreak

Jensen Farms, located in Holly, Colorado grows and ships cantaloupes throughout the United States. After numerous reports of an outbreak of Listeriosis, the FDA and CDC traced the contaminated melons back to this farm. According to a news update from the FDA on Sept. 30, 2011, “the cantaloupes were produced from the end of July to Sept. 10, 2011. Given that the Jensen Farms’ recall has been in effect for more than two weeks, it is expected that all of the recalled whole Jensen Farms cantaloupes have been removed from the marketplace.”

The website for the Mayo Clinic notes that “Listeria infection is a food-borne illness that can be very serious for pregnant women and people with impaired immune systems. Listeria bacteria can survive refrigeration and even freezing.” As of Oct. 1, 2011, the CDC reported that the contamination had been responsible for the deaths of 17 people and the illness of 84 across 19 states.

In response to this outbreak, the FDA noted that “It is very important that consumers clean their refrigerators and other food preparation surfaces. Consumers should follow these simple steps:

• Wash hands with warm water and soap for at least 20 seconds before and after handling food.
• Wash the inside walls and shelves of the refrigerator, as well as cutting boards and countertops.
• Wipe up spills in the refrigerator immediately and clean the refrigerator regularly.
• Always wash hands with warm water and soap following the cleaning and sanitization process.”

Do These Guidelines Prevent Food Borne Illness?

For all of the regulations, safeguards, inspections and, yes, public service campaigns, the growers and processors of food employ humans and sometimes they get careless and make mistakes. Such is also the case with homemakers.

In cases where these mistakes cause deadly diseases to spread, the Food Safe Families campaign could help to ameliorate the damages from contaminated cantaloupes, ground meat, peanut butter or any other food. However, it will have no effect on preventing the disease from starting. That involves many other factors. These include: the distance and the number of companies that must handle food between the farm and family and the quantity and quality of the inspections along the distribution channels.

Given time, the Food Safe Families campaign could have a positive impact on the health of U.S. citizens. Even now, the use of the social networks that were launched for this campaign have served as valuable tools to help with the dissemination of information about the latest contamination. However, such programs as buying foods that are produced closer to home may have more impact.

Patricia Walling
Patricia Walling is a web content designer for several healthcare-related sites. She self-identifies as a perpetual student of medicine, and can be found most of the time researching anything
related to the field. She lives in Washington, and as a result loves the long winters.

Wednesday, October 5, 2011

Ten Biggest Food Recalls in US History - link

I was recently contacted by a reader who included a link to a commercial website.  I would not normally publish such a comment, but this site does contain useful information, primarily for American businesses.

The page she specifically included lists ten very large food recalls in the US.  I'm not sure if they are listed in order of cost, volume of product or effect on consumers, and there is only minimal detail.  However, I have included the link here so that interested readers may search further to obtain more detail on these recalls.

Saturday, September 17, 2011

Cidre with that extra fizz could be a nasty surprise

The UK Standards Agency announced on the 18th September that InBev was recalling three batch codes of Stella Artois Cidre in bottles.  Fruit juices and alcoholic beverages make few appearances in lists of hazardous foods and drinks, and this is the first time they feature in Safe Food.

The problem with these batches is yeast.  Yeast is used in bread making, beer fermentation and, of course, Vegemite, the breakfast spread many New Zealanders were brought up on.  So why is yeast dangerous?

Yeasts convert sugar to alcohol and carbon dioxide.  They put the fizz in beers and sparkling wines.  If this occurs in a controlled fermentation process, there is no problem.  However, if yeasts get into finished products containing sugar, such as bottled fruit juices or alcoholic beverages with residual sugar (not fermented to "dryness"), they can produce carbon dioxide in the bottle.  The cells can generate pressures up to 10 atmospheres - sufficient to burst the bottle.

The recall notice says:
  • handle the bottles carefully, wearing gloves and protective eyewear, to determine if the product is from the affected batch
  • on an individual bottle, the batch code is printed on the bottle’s neck
  • on a 12-pack the batch code can be located on the long side of the pack, to the right of the barcode
If you do have a product from an affected batch, please call InBev as soon as possible on 0800 0731736 between 8am and 8pm. Do not consume or handle the product further.

I once saw a similar recall notice that effectively invited anyone having the affected product not to touch it, but to call the bomb squad!

This may sound a bit melodramatic, but think about this:
One of my winemaking colleagues wanted to produce sparkling wine from a batch of still wine.  He calculated the amount of carbon dioxide to dissolve in the wine and added this to the bottles as small pellets of carbon dioxide ice.  He put corks in the bottles and wired them on and then stored the bottles in a cupboard.

A few hours later, there was a tremendous bang from the cupboard.  He found only the necks and bases of the bottles; the rest was fragments, many of them embedded in the wooden walls of the cupboard.  We could only assume that the carbon dioxide had been slow to dissolve in the wine and the pressure had built up too fast.  This could have been very nasty had he been holding a bottle at the time.

As they say in the extreme sports programmes, "Don't try this at home".

Wednesday, September 14, 2011

Big One becomes Big Seven

Escherichia coli O157:H7 has now been joined on the FSIS most unwanted list by the "Big Six" - other strains of E. coli capable of producing Shigatoxin.

As we saw in May and June 2011 in the German outbreak, Shigatoxin-producing E. coli can cause a potentially deadly food borne infection that can leave survivors damaged for life.  The outbreak also resulted in huge economic loss in several European countries as fresh produce was either banned by authorities or shunned by consumers.

As of the 13th September 2011, these seven strains - O157:H7, O26, O11, O103, O121, O45 and O145 - will not be permitted in non-intact raw beef in USA.  If they are found to be present, the meat must either be destroyed or cooked before sale.

It has been a long road to get to this point. In October 2009, Bill Marler, a US attorney, filed a petition with USDA/FSIS for an Interpretive Rule declaring all enterohaemorrhagic Shigatoxin-producing serotypes of E. coli, including non-O157 serotypes, to be Adulterants within the meaning of the Federal Meat Inspection Act.

Not much has been heard since, though there has been a certain amount of correspondence.  Even the regulatory authorities didn't seem to have a united view.  On the 3rd June 2011, the Deputy Director of CFSAN, Donald Kraemer, stated on the FDA website "FDA considers any disease-causing strain of E. coli in food to be illegal”.  The FSIS deems only O157:H7 to be an adulterant.  Tellingly, Kraemer’s comment was removed from FDA website on 5th July 2011.

The new declaration is being hailed as a victory.  Elisabeth Hagen, head of food safety at the Department of Agriculture, said that this was "one of the biggest steps forward in the protection of the beef supply in some time.  We’re doing this to prevent illness and to save lives.”  A worthy cause.

However, I have some concerns about this optimism.  Will the reclassification of the Big Six make meat safer?  I'm not so sure.  Certainly, if these bacteria are detected in meat, the product will not be allowed on the market unless it is diverted to cooked products.  This may be a challenge for the meat processors - since 1994, O157:H7 in raw ground beef has been declared an adulterant with zero tolerance by FSIS.  In October 2007, the Topps Meat Company recalled 21.7 million pounds of ground beef, bringing the total recalls in the US between April and October 2007 to over 30 million pounds of red meat, mostly hamburger.  A company manufacturing frozen hamburger patties is unlikely to have the capacity to redirect this much meat to a cooking process and there may be difficulties in finding a buyer for the product, so it may have to be destroyed.

Secondly, as far as I am aware, there is no requirement for processors to test for these bacteria.  If this situation doesn't change, the first indication that something is wrong may still be when people start showing up at the hospital with gastrointestinal disease.

Thirdly, the cost of testing is currently very high and the testing may take up to 5 days, even when things go well.  I have already written about the impossibility of guaranteeing safe food by testing.

Finally, testing for the Big Seven will miss any Shigatoxin-producing non-members, as was the case with the German outbreak of O104:H4

The FSIS move is a good start and is motivated by good reasons.  However, the only way that safety of food can be improved is by development of risk management plans and rigorous application of critical control points throughout the food chain, including food service outlets, i.e. farm to fork.  Consumers should not receive contaminated food, but they too must play their part by prevention of cross contamination in the home and proper cooking of foods.  Future posts will deal with some of these approaches.

Where does that leave us with foods like sprouts?  Food for thought.

Since I wrote this article, Shawn Stevens has written an article "Big six declared Adulterants: Is it a good thing?" in, a blog for the meat industry in the US.  It seems that he too has some concerns. You may have to register to read the article, but registration is free.

Saturday, September 10, 2011

"Safe Food" makes the top 50

I recently received an e-mail from Paul Hench, who writes for, a website dedicated to providing students with the information and tools needed in order to pursue their Masters in Public Health. 

Paul has included Safe Food in his top 50 list of food safety blogs.  Though unofficial, this list puts Safe Food alongside blogs that I regard as important sources of information and opinion and it's gratifying to see this recognition.  The list will be a valuable resource, not just for PH students, but for all those interested in food safety.

I have not yet searched the whole list and therefore cannot endorse these blogs, but you may care to check them out for yourself.  Goto:


Wednesday, August 24, 2011

Natural mercury in fish

Most of the posts on this blog are about bacterial food poisoning, so this post is a change on two counts.

Mercury contamination of fish is usually associated with industrial pollution of rivers and estuaries.  William Ray, of Radio New Zealand, today reported that experts have suggested that the levels of mercury in trout in waterways around Totorua are so high, people should limit their intake to one trout per month.  (I wish I could catch so many!).

Rotorua is one of New Zealand's most famous geothermal areas and the experts have suggested that the mercury is from natural hydrothermal sources.  However, it appears that runoff from farms in the area may also be involved.  The nutrients washed into the rivers and lakes cause algal blooms, which lower the dissolved oxygen content of the water.  This in turn allows transfer of mercury from mud into the water, from whence it enters the food chain.

Perhaps the most infamous mercury poisoning occurred in the Japanese city of Minamata, which gave the name Chisso-Minamata disease to the resulting neurological syndrome.  The Chisso Corporation chemical factory released methyl mercury into the Minamata Bay and this highly toxic compound was accumulated by fish and shellfish.

The Rotorua trout have also accumulated mercury, but Dr. Ngaire Phillips from the National Institute of Water and Atmospheric Research points out that the recommendation for consumption of no more than one trout per month is based on a lifetime consumption.

Saturday, August 13, 2011

Listeria and bacon recall

I was just scanning the news and did a double take.  An Ontario company, Aliments Prince, S.E.C., has just recalled 380,000 lbs of bacon because of possible contamination with Listeria monocytogenes.  That's a lot of bacon!

It seemed to me that this was excessively cautious.  L. monocytogenes should not be found in a food product that has been processed in such a way that the bacteria should not survive, but the organism can occasionally be found in foods that have not been given a listericidal process.  So green leafy vegetables and other raw foods may occasionally contain L. monocytogenes.  The bacteria can be found in many parts of the environment, such as surface water, soil and decaying vegetation, and it's not surprising to find it turning up sometimes in raw foods.

On closer reading, it turns out that the FSIS found a sample of cooked diced bacon from Aliments Prince contained the bacteria.  This is a whole new ball game - the product could be expected to be consumed without further heating and thus could put at risk susceptible consumers.  See my post "Listeria Hysteria" for further information.

The company has done the right thing.  We can't avoid occasional low levels of contamination of raw foods by L. monocytogenes, but something has gone seriously wrong when we find it in cooked foods.  Either the process given was too mild, or, much more likely, the product has been recontaminated post processing.

Tuesday, August 9, 2011

Haemolytic Uraemic Syndrome

In the wake of infection by Shigatoxin producing Escherichia coli (STEC), some patients develop Haemolytic Uraemic Syndrome (HUS).  The recent outbreak of O104:H4 STEC in Europe resulted in an unusually high proportion of patients going on to develop the syndrome, some of whom succumbed to the infection.

Drew Falkenstein, an associate of Marler Clark law firm in Seattle, has written a very well informed article on HUS.  Rather than write another, I suggest that interested readers follow the link to Drew's posting on Food Poison Journal.

Wednesday, July 20, 2011

Hello, how are you, is it seeds you're looking for?

It's all over, bar the shouting.  Or is it?

As at 30th June, 2011, there were 50 reported deaths from the Escherichia coli O104:H4 outbreak centred in Germany.  Cases of illness have been reported from 16 countries, not all victims having travelled to Germany.  This suggests that there may have been some person-to-person infection, though in at least one case, there appears to be none of these links.

Thankfully, the number of cases reported is dropping, the outbreak following a classic curve of increasing number of cases, followed by a decrease once reporting shows that there is an outbreak under way and information and preventative measures become available.

European scientists and government sources have suggested that  fenugreek seeds imported from Egypt in either 2009 or 2010 are implicated in the outbreaks in Germany and Bordeaux.  Epidemiological investigations do link these particular sprout seeds with the outbreaks.  But a link is not proof.

Not surprisingly, the Egyptians have objected to their seeds being blamed for the outbreak.  I have some sympathy with them - as far as I am aware, O104:H4 has not been isolated from any seed samples.  If these seeds are the source, then we have another problem on our hands.

If the seeds were imported to Germany and France, and perhaps other countries, the implication is that any E. coli O104:H4 present in the seeds survived for between two and three years before the sprouting process allowed them to multiply and cause the outbreak.  This raises a number of questions:  is this strain of E. coli particularly hardy, so that it can survive for years in dry seeds?  Were all the infected seeds exported from Egypt?  If not, were there any O104:H4 cases in Egypt between 2009 and the present?  If there were cases, why have we not heard about it?

I don't believe that we have heard the last of this by a long chalk.

Friday, July 8, 2011

Mud hoppers

This post is not directly about food, but it is about eating stuff.

Over the last weekend, an annual event was run (well actually, quite a bit of it was crawled) over a 6km course in Auckland.  Nothing unusual about cross country running in New Zealand, but this one involved obstacles to crawl under or climb over and a very large amount of mud.  Two TV news presenters took part, so there was plenty of footage to analyse.

I am all for active sports, but I wonder how many of the competitors will regret the weekend's activities, and not just for sore muscles.  At one point, the competitors crawled, sploshed or "swam" though a trench full of thick mud.  At least one competitor dived headfirst into the mud as if he were diving into the surf.  None of the participants could have avoided getting some of the mud in their mouths.

Soil is interesting stuff - it's the goto place for microbiologists if they need to isolate a microorganism that has a particular characteristic; it's one of the best sources of bacteria.  If animals have been grazed on the paddock, or water in the mud has drained from a farm, it is likely that the mud will contain many faecal organisms.  In 2008, there was a significant outbreak of campylobacteriosis after a mountain bike race, in which competitors got very muddy.  None of the support crews became ill.

I'm sure that mud running allows us to relive our childhood without being scolded for getting dirty and it's certainly a good spectator sport, but competitors should be aware of the risks associated with eating the stuff.

Saturday, July 2, 2011

Can we control toxigenic E. coli?

Last week at the New Zealand Institute of Food Science and Technology annual conference, I presented a paper on non-O157:H7 shigatoxigenic E. coli.  That's a bit of a mouthful, if you'll pardon the unfortunate pun.  These bacteria have gained the ability to produce a toxin that can destroy intestinal epithelial cells and also damage the kidney.  E. coli O157:H7 is probably the best known of the Enterohaemorrhagic E. coli  (EHEC) types.  The strain causing the outbreak in Germany and other parts of Europe is a non-O157 type and indeed appears to be from a different group - the Entero-Aggregtive EC.

During the session, two other papers were presented, one on Cronobacter sakazakii - the neonate nasty, and one on Salmonella.  All three presenters talked about control of these food borne disease-causing organisms.

During the discussions, it became apparent that there was some difference of opinion on the effectiveness of control measures during production and processing of foods.

For example, the poultry industry in New Zealand has been remarkably successful in controlling Salmonella in poultry flocks by strict management of biosecurity, and thus eggs and chicken meat are essentially free of Salmonella.  Unfortunately, these controls have not worked for Campylobacter and there is still a significant rate of C. jejuni illness that can be traced to poultry, though this rate has fallen over the past two years.

Similarly, when I suggested that control of Salmonella would likely also control E. coli, a friend and colleague stood up and said that these two organisms are significantly different and controls would need to be tailored to each.  I invited him to come outside and we'd sort it out by fisticuffs!  However, it became obvious that we were talking at cross purposes and we were both right.

Salmonella, Cronobacter and E. coli are all vegetative bacteria.  That is, they do not form spores and are not particularly heat or chemical resistant.  Thus, during food processing or in the hands of the consumer, control is easy - heating to about 75-80C for a few seconds will kill them all.  If we prevent cross contamination, then the finished food will be safe to eat.

It is much more difficult to set conditions during primary production that will control these bacteria.  Vegetables are usually grown in soil.  They therefore become contaminated with soil organisms.  Even hydroponic growing systems may become colonised by bacterial biofilms and thus contaminate the products.  Animals and birds all carry populations of bacteria in their guts or on hides, hair, feathers and feet.  It is impossible to eradicate these bacteria, so they must be controlled during processing. 

But what do we do with vegetable sprouts?  These products must be regarded as hazardous - they are grown in conditions of high humidity and at temperatures that support the rapid growth of bacteria.  If pathogens, such as E. coli O104:H4 are present in the seeds, in the water or the equipment, they can grow rapidly.  Stir-frying will probably kill the bacteria, provided the temperature gets high enough.  Sprouts are also eaten raw, so there is no controlled lethal process step and the consumer ingests the bacteria, sometimes with fatal results.  If people are to continue to eat raw sprouts, we need to develop some means of decontaminating them, such as a rinse in a bactericidal chemical solution.  Nothing is perfect, but control of production, processing and distribution, together with consumer education, should decrease the likelihood of a similar outbreak to that currently occurring in Germany.

Friday, June 24, 2011

Gloves don't make you bombproof

This week, my wife watched a professional catering company setting out a room for conference meals.

One of the girls was setting out plates with her bare hands.  She then returned to the room with plastic wrapped bananas on a pile of plates.  She was wearing one plastic glove and contrived to remove the plastic wrap from the bananas with the ungloved hand.  She then carefully separated the individual bananas using the gloved hand.

What did this achieve?  I don't have a major problem with the plates being set out with bare hands, provided she washed her hands before she started.  The wrapped bananas were in contact with the plates, so anything on the plastic wrap might also be transferred to the plates.  Unless the girl was a part-time juggler, it's likely that she touched the banana skins with her bare hand as well as with the gloved one.  But people don't eat the skins and anyway, how many hands had touched the skins during harvesting and transport?

Many years ago, when I first started teaching food microbiology, O.P Snyder used to write regularly about the hazards associated with handling food with bare hands or with gloves.  He argued that the use of clean hands was less hazardous than unchanged gloves.  The critical words here are "clean hands".

There is no doubt that contamination can be transferred by manual handling of food.  Some regulatory authorities require that food handlers wear gloves and do not permit contact between bare hands and ready-to-eat foods.

However, simple observation in kitchens and service areas show that many food handlers do not know how to use gloves to improve food safety.  Chefs often use their fingers to assemble food; counter staff handle food while wearing gloves and then clean the counters before going back to handling food without changing the gloves.  When gloves are changed, are the hands washed?  Usually not, so hands that have become sweaty inside the gloves are then used to put on the fresh gloves and must inevitably transfer some bacteria to the new gloves.

Dirty gloves are just as dirty as dirty hands.  Wearing gloves does not make you bombproof - you have to keep your brain engaged when handling food.

I look forward with interest to the discussion that this post is bound to generate.

For more information on gloves in food service, go to: 

Friday, June 17, 2011

Colonel Mustard, in the Dining Room, with the Sprouts

The last couple of weeks have been like the old game of Cluedo, with everyone running round accusing various participant of foul play and trying to find the culprit.  It would be amusing if it were not so deadly serious.

It now appears that the outbreak of Escherichia coli O104:H4 in Germany, which has now reached 16 countries, was probably caused by fresh vegetable sprouts grown in a farm in Uelzen, near Hamburg.  Unfortunately,  cucumbers from Spain, lettuces and tomatoes also had the finger pointed almost indiscriminately at them.  That caused huge financial losses for the suppliers and had knock-on effects on vegetable sales throughout Europe.  In some ways, I can sympathise with the authorities and the media.  This is one of the largest and most serious outbreaks of food poisoning ever and finding the source as quickly as possibly was imperative.

At the time of writing, there have been 3517 cases of EHEC infection, resulting in an unprecedented 839 cases of Haemolytic Uraemic Syndrome and 39 deaths.  The rate of new case reporting has slowed, but it is likely that more people will become ill before this is all over.

This shows just how difficult it is to pinpoint the source of an outbreak of food poisoning in our highly integrated and widespread food supply chain.  The sprout farm purchased seeds for sprouting from both European and Asian countries.  The seeds were sprouted, using what seems to be standard and well designed conditions, and the 18 different sprout mixtures were sent to many different points in Germany.

The German authorities have been accused of being in disarray and having no proper response prepared.  There may be some truth in this - if the responsibility for food safety is spread across many local authorities and agencies, setting up a coordinated and timely response is fraught with difficulty.  But it is generally recognised that epidemiological investigations may have a success rate as low as 33% in tracking down the source of infections and the chance of success falls as time goes on.

At times like this, we often hear calls for increased testing of products before they are released onto the market.  Good try, but no cigar!  For a number of reasons, microbiological testing to assure safety of food is just not possible.  Testing is expensive and time consuming.  In some cases, the testing period exceeds the shelf life of the product.  A simple statistical calculation shows that when contamination levels are low, the number of samples that must be tested to get even a 95% chance of detection is prohibitively large and even then, 5% of contaminated samples will be accepted as safe.  Testing for E. coli O157:H7 would not have picked up the German strain and even proposed widened testing for "The Big Six" Entero-Haemorrhagic E. coli strains would have missed this one.

Regulators must be strong in the coming months.  Microbiological testing gives only a retrospective view and a poor one at that.  Imposing increased mandatory testing will not assure the safety of foods.

The only way we can ensure the safety of our food supply is to introduce controlled lethal steps in processing, such as heating or irradiation, or to put in place rigorous control of every potentially hazardous ingredient, process step, processing facility and distribution chain.  This is particularly important with high risk products such as sprouts.  What every food producer and distributor needs is a Hazard Analysis based Food Safety Programme of Risk Management.

Monday, June 6, 2011

Is it sprouts now?

German authorities have now identified sprouts as the putative source of the outbreak of Escherichia coli O104:H4 food poisoning.

This is not the first vegetable claimed to have been the cause - lettuces, tomatoes and Spanish cucumbers have all been suggested as the source, apparently with poor justification,  at one stage or another during the outbreak.  Of course, this has stigmatised the growers and in fact has seriously damaged the whole fresh vegetable market in Europe.  The American military has ceased purchase of any European vegetables for the military commissaries and may arrange an airlift of fresh vegetables from America, thus contributing to global warming and misery for European vegetable farmers. 

I'm not going to comment further on the possible source of the outbreak until I see Pulse Field Gel Electrophoresis data linking bacterial isolates from the sprouts and the patients.  This will still not prove that the sprouts are the source, but if the PFGE profile matches, it is strong evidence for a finding.

Friday, June 3, 2011

How do you trace an outbreak? With difficulty!

The outbreak of E. coli O104:H4 food poisoning in Germany is possibly one of the worst outbreaks on record and certainly one of the most deadly.

Public health officials still don't know the source.  Spanish cucumbers were initially blamed, but it appears that might have been wrong, though it does appear that salad vegetables may have been involved.

The investigation of outbreaks like this is a science in itself, but must be frustrating for epidemiologists.  Our modern supply chains are extremely complex - foods are sourced from all over the world and suppliers may make up orders from many different primary producers.

"...real life does not have tidy TV endings. Despite determined efforts and great expense, the precise source of poisoning is found in fewer than one-third of outbreaks. But here is a quick look at how public officials try to resolve those puzzles. 

First, there is a trigger event – usually people showing up in emergency rooms with violent cases of diarrhea and vomiting that are the hallmarks of food poisoning. Samples – stool, saliva, sometimes blood – are taken. Serious illnesses like E. coli get special attention: 
Reporting them to public health authorities is mandatory.

Data from lab tests are routinely sent to local public health authorities and to PulseNet, an electronic database. While most cases of food poisoning are sporadic, patterns can be spotted quickly – there can be a cluster in a single city, or a sudden spike over a wide geographic area. Labs do DNA fingerprinting of pathogens like E. coli that can show if the illnesses have a common source. 

In this instance, three deaths of patients with E. coli infection in Germany set off alarm bells. They all had the same DNA fingerprint, strongly suggesting a common food source.
When an outbreak is suspected, epidemiologists (disease detectives) start questioning those who are sick. In these “hypothesis-generating” interviews, patients are asked about specific high-risk foods (such as sprouts or unpasteurized milk) and for detailed recollections of what they have eaten in recent weeks. 

This can produce, fairly quickly, a list of suspected culprits. E. coli is a fecal bacterium, for example, so raw foods are a focus. In Germany, a day after the deaths, consumers were warned to not eat tomatoes, cucumbers or lettuce. Three of four cucumbers tested came from Spain, so the country was quickly identified as a culprit in media reports. 

Public health officials share information gathered from patients with food safety regulators (such as the Canadian Food Inspection Agency), who try to trace the commercial supplier of a common food source. 

In their interviews, epidemiologist collect information on where food is purchased; if many of the patients shopped at the same food chain, for example, the CFIA would identify their vegetable suppliers and try and trace the movement of food through distributors and back to the farm. 

But there can be hundreds, even thousands, of suppliers and contamination of food can occur at any point in the process of getting food from the farm to the table – during production, processing, storage, distribution or preparation.  Finding the “locus of contamination” becomes an almost insurmountable process of elimination. Currently, farms in Europe that produce vegetables that are consumed raw are being set upon by all manner of investigators who will test products, water sources and so on. 

The paradox is that the more people get sick, the easier it is to ultimately find the culprit because the number of food sources they have in common becomes smaller. Often, despite mountains of data, the leads run cold. But the demand for answers does not wane.
The challenge for public health officials and regulators is finding the right balance. They issue speculative warnings like “Don’t eat Spanish cucumbers,” but more often than not they are wrong, and that can cause grievous damage to food producers. 

At the same time, acting slowly and waiting for a definitive answer on the source can result in countless cases of illness and death, and still no definitive answer. 

To read the full article and access the video clips, click here.

Not all reporting is of this quality; even the BBC has broadcast a news item labeling E. coli as "a virus".  Didn't the reporter talk to an expert, or even a Level 6 food science student?

Thursday, June 2, 2011

Evolution in action

Over the last three weeks, a rare form of Escherichia coli has made an appearance in Germany.

E. coli is a normal inhabitant of the gut of man and animals and is found there in very large numbers.  They are mostly harmless and actually help us by producing vitamin K.  However, some strains are pathogenic and cause diarrhoea.

Individual strains are recognised by their antigenic signature. The antigens are found on the surface of the cells, on the flagella and in the capsule that surrounds the cells.  Thus one of the strains that hits the news quite frequently is referred to as O157:H7.

The strain now causing havoc in Europe is E. coli O104:H4.  This has rarely been seen as a cause of disease.  However, the current outbreak is shaping up to be one of the most dangerous ever seen.

Why has this happened?

That's a question that none of us can answer yet, but the information on this strain is growing rapidly.  It can produce a very damaging toxin, called Shigatoxin.  The bacterium causes bloody diarrhoea, which is bad enough in itself.  But bacteria producing this toxin can also go on to produce Haemolytic Uraemic Syndrome, normally affecting around 2 to 10% of patients, who are often very young or immunocompromised.  However, O104:H4 appears to be very virulent and around 30% of patients, who were not in the high risk group, have developed this life-threatening syndrome.  So far, 18 people have died.

The fact is, bacteria evolve very rapidly.  We see one strain develop resistance to an antibiotic and soon other strains become resistant too.  This happens because bacteria can  exchange genetic information by a number of different mechanisms.  The rate of mutation might be very small, perhaps one in 10 million replications produces a mutant and most of these mutations are probably lethal.  However, a single cell can potentially produce a population of around 17 million cells in 8 hours.  That allows for a lot of mutations.  If even one of these mutants has some advantage over the rest of the population, or at least no disadvantage, the mutation will spread through the population.

This might surprise you, but bacteria also suffer from virus infections.  These viruses, or bacteriophages, invade the cells and cause them to make more virus particles before bursting open to restart the infection cycle.  Occasionally, the new virus particles contain a bit of bacterial DNA and transfer it to the next host.  Sometimes, whole genes can be transferred.

It appears that O104:H4 has not only the Shigatoxin gene, almost certainly transferred by bacteriophage, but has also picked up some other virulence factors.  This is why it is so dangerous - the toxin is very damaging to human cells, particularly in the kidney, and the bacterium appears very capable of initiating infection.

I believe we are seeing evolution in action.  A normally benign bacterium has become a killer.

Thursday, May 26, 2011

Sarah Carter - confusion reigns

On 12th March, 2011, I wrote about the tragic death in Chiang Mai of Sarah Carter.

Originally, her death was blamed on consumption of toxic seaweed.  At the time, I suggested that this was a highly suspect conclusion, based on the symptoms and the circumstances.

A short while later, it was claimed that Sarah and her two friends had been infected by an ECHO virus.  The symptoms matched.

However, more information came to light - a Thai tourist guide had died in the next room in the same hotel and a week earlier, two other tourists had died in a room one floor below. 

The New Zealand TV3 channel discovered that a total of seven tourists had died in Chiang Mai in similar circumstances.  Sara Hill, an investigative reporter for TV3, went to Chiang Mai and made a programme screened here a couple of weeks ago.

In an interview with Sarah Carter's friend, Sara Hill discovered that none of the three girls had eaten seaweed and had eaten two different meals.  They all developed sore stomachs and vomiting and were hospitalised.  According to a Thai cardiologist, Sara Carter suffered very low blood pressure, dehydration and low blood flow to the kidneys, with ultimate kidney failure.

The reporter managed to obtain swab samples from the room occupied by Sarah and returned them to New Zealand for testing.  Traces of chlorpyrifos, an organo-phosphorus insecticide used in corn and cotton farming, were found in the swabs.  Dow Chemical Company voluntarily withdrew the registration of chlorpyriphos for domestic use in 2001.  Mr. Ron McDowell, a UN scientist, hypothesised that Sarah had been exposed to chlorpyrifos as a result of over-zealous spraying of the hotel room to control bed bugs by a pest control operator.  McDowell claimed that the symptoms and pathology all fitted with chlorpyrifos poisoning.

However, the swabs were taken three months after the room was occupied by Sarah, so spraying could have occurred at any time during those three months. The report form was shown in the programme.  The level in Sarah's room was given as <0.1 microgram/sample, which probably means "below the limit of detection".  A sample from an air conditioner was 0.24 micrograms/sample, but the film of the sample being taken suggested that the area swabbed was uncontrolled.

The half life of chlorpyrifos in the human body is about one day, so, although it is absorbed quickly, it also disappears from the body quickly.  Thus tests at the hospital may not have shown its presence in Sarah's body.

I'm not convinced that we are much further forward.  The Thai authorities were not being particularly cooperative with the TV3 investigation and recently refuted the chlorpyrifos theory.  Three toxicologists in New Zealand have issued a statement criticising the programme and the conclusions drawn by the experts consulted by Sarah Hill.

It looks as though seaweed is off the hook and food poisoning seems a bit unlikely, as the three girls ate different meals, but suffered similar symptoms not commonly seen in microbial food poisoning.  Food contamination is not completely ruled out, as several meals could have been contaminated with a chemical.

I don't know if we will ever know the true story

Friday, May 13, 2011

Kiwifruit dumped

It's been a mixed year for New Zealand kiwifruit growers.  Earlier in the season, some vines were found to have been infected by Pseudomonas syringae pv actinidiae (Psa) - a bacterial disease first identified in Japan about 25 years ago.  The Asian strain causes leaf spotting and some die-back of vines, though it is far less savage than the Italian strain that has also been found in one area.

In the last week, 100,000 trays of kiwifruit have been withdrawn from the market (some had already been shipped and will be intercepted) and will be destroyed.  It appears that a worker on a harvesting gang has been diagnosed with typhoid, picked up overseas before arrival in New Zealand.  Since it is not possible to isolate the specific fruit handled by the worker, all the fruit picked by that gang has been withdrawn.

The risk of infection being carried on the fruit is very low, but Zespri, the main marketer of New Zealand's $1.5 billion kiwifruit export industry, has been cautious and manned up, taking the pro-active response to prevent any possible disease risk for consumers.  This action is in stark contrast to those of some overseas companies that have attempted to conceal the potential of their products to cause harm to consumers.

The value of the withdrawn fruit is around $800,000 and represents less than 0.1% of this year's expected kiwifruit exports.  However, the unfortunate growers may not be insured, so this will be a serious loss to some orchardists.

Tyhpoid is caused by Salmonella enterica enterica, serovar Typhi, a bacterium that infects the intestine, resulting in damage to the intestine and fever.  Resultant diarrhoea can lead to transmission of the bacteria to other people and the environment.

The disease was named from the spike in infections observed after severe typhoons.  The contaminated water and poor sanitary conditions that followed the typhoons provided the conditions for increased numbers of infections.

  Mary Mallon was an itinerant cook, having arrived in America around 1874 from Ireland.  She became a domestic servant and eventually a cook in New York.  Though she appeared healthy, between 1900 and 1907, Mary had seven cooking jobs where 22 people  became ill and one died of typhoid.  After an investigation, Mary was taken by force and held against her will without trial.  This occurred at a time when the symptomless carrier state was unknown, so the investigation was quite innovative.  Mary was effectively imprisoned under sections 1169 and 1170 of the Greater New York Charter and lived alone in a cottage on North Brother island.

After her release, Mary eventually went back to cooking and this time was sent to the island for a period of 23 years, which ended only when she had a stroke.  She died six years later.

Mary was then and is still known as Typhoid Mary.

If you want to read more about Mary Mallon, go to Jennifer Rosenberg's 20th Century History page:

Sunday, May 8, 2011

Hazard or Risk?

The words "Hazard" and "Risk" are often used rather loosely in everyday speech. e.g.  "Cycling to work in Auckland is a risk". What does this mean?

I read an article today that attempted to clarify the situation.  Unfortunately, the writer got it wrong and increased the possible confusion.

In terms of food safety, a hazard is something that has the potential to harm the health of the consumer, such as the presence of a piece of glass in a cheesecake.  Hazards may be biological, chemical or physical.

The risk is the probability of the hazard occurring.

The other thing we need to consider is the severity of the outcome.

Let's take a non-food example to show the importance of understanding these terms.

The hazard under consideration is getting hit by a wheel falling from an airliner.

We know that the risk (probability) of this happening is very low.

But if the event does occur, the severity of getting hit by falling debris is very high, possibly lethal.

Now think about hazard, risk and severity in the food safety context.

Saturday, April 30, 2011

Walls have ears and bacteria have antibiotic resistance

Recently, I was having my lunch at a conference and couldn't help overhearing a conversation between two people sitting alonside me.  I suppose I should have tried not to listen, but their discussion was in my own field.

It appeared that one of them had read a survey conducted on the bacteria isolated from poultry in USA.  Even "organically grown" chicken contained bacteria that displayed multiple-antibiotic resistance.  This implies that the chicken farms may be using antibiotics in the flock rearing operation, though it doesn't necessarily prove the point.

Without getting into the rights and wrongs of using antibiotics in rearing of "organically grown" poultry, this does point to a wider concern: that farmers may be using sub-therapeutic levels of antibiotics widely to improve growth rates and yields of all meat animals.  Any bacteria that survive and grow in the presence of antibiotic are likely to be resistant to the chemicals and if these bacteria should go on to infect humans, those antibiotics will be useless for treatment.

I'm not sure if these people were talking about a survey*** conducted by the Translational Genomics Research Institute (TGen) in Arizona.  These scientists tested 136 samples of 80 brands of beef, chicken, pork and turkey collected from 26 retail stores in five US cities.  They found that nearly half of the samples contained Staphylococcus aureus and that just over half of these isolates were resistant to at least three classes of antibiotics.  Further analysis suggested that the bacteria were from the animals and not from the processing factories, again indicating that antibiotics had probably been used in rearing the animals.

It might make meat more expensive, but I believe that governments must force the reduction in the amount of antibiotics used in animal rearing if we are to avoid catastrophic consequences for the human population in the near future.  Remember: it has been estimated that the cost of getting a new drug onto the market is now between 2 and 3 billion dollars.  We aren't going to get many new drugs at that rate.

*** The full report is available at:

(The report is a technical report, intended to be read by other scientists, but anyone should be able to follow the discussion).

Friday, April 15, 2011

Tasty but occasionally dangerous

If I asked you to name a food group that might be implicated in food poisoning, you would probably respond with "meat".  I did a survey (n=1) at home today and got that answer.  My wife thought a bit longer and said "Custard, but that's only because you have influenced me over the years".

Baked goods probably don't spring to mind as potential carriers of food poisoning bacteria.

In the last week, there have been reports from Rhode Island of zeppole, or St. Joseph's Day cakes, causing food poisoning by Salmonella.  I had never heard of zeppole before this report, but they are apparently popular in Italy, Sicily and Malta and in the Italian-American communities in the United States and date from the early 19th century.  They are deep-fried dough balls, or sometimes choux pastry, topped with powdered sugar or filled with custard, pastry cream or a mixture of butter and honey.  They sound delicious, though perhaps dangerous for the figure!

At the time of writing, there have been 76 cases and 29 hospitalisations.  Two people have died from Salmonella-associated illness.  It is too soon to say how this happened, but the possibilities include a carrier of Salmonella working as a food handler, or the use of ingredients contaminated with Salmonella.  The deep-fried pastry would probably be sterile immediately after frying, but could be contaminated by the food handler during the filling process.

Breads, fruit cakes and biscuits are usually pretty safe by virtue of low water activity, but filled pastries receive quite a lot of handling, while real cream may be contaminated with bacteria that rapidly grow under abuse temperatures to the point where they can cause food poisoning, either by infection or intoxication.

Monday, April 4, 2011

Will spoiled food make you sick?

I recently received a message from Jo, asking me to comment on this subject.  Jo actually raised a lot of questions and, of course, the answers are not simple.

First question:  If the food smells off, tastes bad, has a poor colour etc. is that a good indicator it will make you sick?

Humans have been on the Earth for a long time and one of the reasons they have survived for so long is that they have evolved self preservation mechanisms.  If the food smells off or doesn't look right, there is a chance that it is poisonous in some way and we tend to avoid it.  Sometimes I wonder what the first people to taste durian or blue cheese thought they were doing!  So, clearly, the answer has to be a qualified "Yes, it might make you sick, but some sort of tribal wisdom suggests that a few foods can look and smell awful but still be OK to eat".

Jo then went on to say that she thought that the food was unlikely to make you sick, as the changes were caused by spoilage bacteria and enzymatic reactions, which are not the same as pathogenic bacteria, which she thought do not alter the food in the same way.

This is where it gets complicated.  Spoilage bacteria do cause some changes, which, by definition, make the food unacceptable to most people.  Other bacteria, such as Salmonella, may grow alongside the spoilage bacteria.  When the food is eaten, the salmonellae  set up an infection in the gut and produce the familiar food poisoning symptoms.

Second question: Is it true that pathogenic bacteria don't alter the food?  Again, it depends on the bacteria.  Generally, clostridia alter the food a lot, producing many smelly compounds and gas.  This would put most people off eating the food, so they would be safe.  But some Clostridium botulinum strains are non-proteolytic.  That is, they don't break down proteins and they don't produce the foul smells that the proteolytic strains make.  So you could find improperly processed canned foods that appear quite normal, but could kill you.

Jo's third question was perhaps the most fascinating: she was most interested in how the food could potentially have both types of bacteria on it near to the time it was made and correctly identified contamination of the food as the cause, possibly by cross-contamination from some source.  A good example would be a careless food handler.

At this point, the food could cause food poisoning if consumed - Salmonella transferred from raw meat to a cream pastry would be a good example here.

Jo went on "However as time goes on and assuming the food gives them all the things they both need to grow, is it as simple as the pathogens might be around for a short time until the spoilage guys, who being better competitors for resources, take over; so by the time the food
is showing signs of being spoiled, the pathogens have been killed off?"

That's a really insightful comment.  Many fermented foods are actually safe because of this pattern.  Take raw cabbage and make sauerkraut:  we shred the cabbage and add about 2.5% salt to it and then press it into a container and seal it.  The salt draws out the tissue fluids from the shredded leaves and bacteria naturally on the leaves begin to produce lactic acid.  If we sample on the first day, we can find all sorts of bacteria, including Escherichia coli and possibly Salmonella.  However, as more acid is produced, the pH falls and the potential pathogens die off.  Finished sauerkraut has a pH around 3.1 to 3.7 and is perfectly safe to eat, though there has been a lot of bacterial growth in it.

So, to return to Jo's original question, "Is spoiled food potentially safe to eat, even though it looks and tastes awful?"    Sorry Jo, I can't answer that.   But if it tastes awful, why would you want to eat it?

One last point:  there is an anecdote that a lady opened a can of peas and thought that they looked a bit different.  She tasted one and cooked the rest.  She died of botulism.  Ironically, if she had cooked them and then tasted one, she would have lived, as the botulin toxin is heat labile.  I don't remember where I read this - it was somewhere around 1980, but it's a good example with which to finish this article.

Sunday, March 27, 2011

Poor Understanding - Raw Milk in New Zealand

Last week, I read an interesting article by Jill Galloway in the Manawatu Standard entitled "Selling milk as it was meant to be".  The story was about the increasing sales of unpasteurised and non-homogenised milk at the farm gate.  Unfortunately, the author and/or her interviewees made a number of errors.

Under New Zealand law, sales of raw milk from the farm gate have been permitted for several decades.  All other milk and milk products must be pasteurised or given an approved alternative treatment. Section 11A of the Food Act 1981 allows for producers to sell up to five litres of raw milk at any one time from their farm gates to people who intend to consume it themselves, or to provide it to their families.  However, the milk must be harvested under an approved Risk Management Programme under the Animal Products Act 1999.

So if farmers follow the rules, there should be no problem about safety.

However the article went on to express some strange views.

For example: "People believe in the integrity of food.  People want to know where it comes from. Processing destroys dairy products".

Or how about: (Farmers) "are up against rules, regulations and science".

But my favourite was:  "Before processed milk, there was no heart disease. Homogenisation means the fat particles are small enough to be ingested, not digested, and go straight through to the blood and arteries," Ms M. says. She thinks homogenisation began because people thought the fat on the top of milk was bad and they did not want to see it.

Hang on a minute.  If Ms M. is correct, then the dairy companies are actually delivering what consumers are demanding.

Second place goes to Farmer C: "When it is pasteurised, the milk becomes dead. People don't want to be eating or drinking dead stuff."

So you never had a steak, Mr. C?

I guess I should not poke fun at these people, who genuinely believe that their product is better than pasteurised milk.  And indeed, they are producing their product according to the NZFSA regulations.  But it does worry me that people can be so smart in some aspects of their lives but authoritatively make such ignorant statements.