Listeria in smoked salmon - again.

The Department of Health in Australia is investigating three separate cases of Listeriosis apparently associated with smoked salmon.  There have been two deaths and one

This is not a reason to stop eating smoked salmon, or even cause for a massive recall.  There is a couple of things we all need to know.

Firstly, no specific smoked salmon product has been recalled.

Secondly, the three cases were in three different states and occurred over the period 22nd February to 7th June.  i.e. they were well separated both in location and time.

Thirdly, and probably most importantly, all three patients were over 70 years old and had other health conditions that may have predisposed them to infection by Listeria.

This is a reminder that people who may be susceptible to listeriosis should avoid foods that are known to carry higher risk of infection.

See:  https://foodsafetywithjaybee.blogspot.com/2011/01/listeria-hysteria.html  and search the blog using keyword Listeria.

McDonald's screen of death. I remain unsurprised.

A recent post from IFLScience.com claims that microbiologists from London Metropolitan University conducted swabbing on touch screens in McDonald's restaurants in London and Birmingham, finding coliforms, Bacillus and Listeria.  They also found Staphylococcus, Pseudomonas, Enterococcus faecalis and Klebsiella.

All of these bacteria are capably of causing infections, and you will find some discussion of these bacteria on this blog site - see labels.

But should we be surprised and should customers at McDonald's be concerned?  Well, I am not at all suprised.  If a microbiologist conducts swabbing in any public place, such as a supermarket, they will find all of these bacteria, perhaps on trolley handles, push plates on doors, in the toilets etc.  As for the customers, if they are concerned, they could order their meal on the touch screen, then wash their hands, or use a hand sanitiser.  Be honest - if you go to any fast food joint after you have been shopping in the mall, do you always wash your hands before you eat?

The original research was done for Metro (see https://metro.co.uk/2018/11/28/poo-found-on-every-mcdonalds-touchscreen-tested-8178486/).   Not surprisingly, when this post was published on FaceBook, there were 1.2 thousand comments and nearly a thousand shares.  My personal opinion is that this article was written and published for shock value and to boost circulation.  Interestingly, a video clip posted on this same site showed that the majority of customers were not surprised by the findings and would still go and purchase food there.

Whatever you think of McDonald's or any other fast food outlet, in my opinion, the researchers are making a mountain out of a molehill, and IFLScience is making it worse.  Don't pick on just one fast food chain, and think about how you protect yourself and your family from infection.

And while you are at it, think about a similar scenario in your own home.

Food for thought:  How do you recognise the microbiologists around you?  They are the people who use their little fingers or elbows to open doors, use a paper towel to turn the taps off in a public washbasin, use a knuckle on the touch screen and who often use hand sanitiser before eating in public.

Listeria strikes in Hawke's Bay, NZ

The news service Stuff has reported that Listeria has caused one death and contributed to another between May and June this year in Hawke's Bay, New Zealand .  At this stage, two other people have been infected, but have recovered.  It is not clear where the infection came from, though there is circumstantial evidence that pre-packaged ready-to-eat meat may have been involved.

Investigation of this type of food poisoning is very difficult.  The great majority of the population will not become ill from exposure to Listera.  In the two deaths, the women were 60+ and 80+ respectively and both were apparently immunocompromised, putting them in a more susceptible group.  The infection can take up to a few weeks for symptoms to show, making it unlikely that patients can remember what they ate and even more unlikely that samples remain for testing.

Listeria is capable of growing at refrigeration temperatures, so cooked and ready-to-eat foods should be stored for only one or two days.  Of course, this poses a problem with salad vegetables, which are not going to be cooked before consumption.

The only real way to combat food borne listeriosis is to be very careful in handling foods, prevent cross contamination between raw and cooked foods, wash fruits and vegetables thoroughly and keep utensils, chopping boards and hands clean.

If you are at risk - pregnant, already unwell, immunocompromised, elderly etc. it is better to eat freshly cooked foods, pasteurised dairy products, canned foods, bread and baked goods without cream, cereals and beverages such as tea, coffee or beer, which have all been heated during production.

You can find more articles on Listeria in this blog by typing "Listeria" in the search box at the top left of this page.

Bacteria in canned food

Looking through the search terms that produced hits on Safe Food this month, I came across "Listeria in canned food".

Is canned food hazardous from the point of view of Listeria?  In my opinion, the answer is "No" with just one small caveat:  "unless the food has been grossly underprocessed, or post- processing contamination has occurred".

Canned foods are divided into two main categories: Low Acid (LACF) and Acid Canned foods (ACF).  The dividing line is pH 4.6, low acid foods having a pH greater than this, and acid food having a pH lower than 4.6.

The significance of this pH value is that Clostridium botulinum can grow at pH above 4.6. 
C. botulinum is able to form very heat resistant spores and can grow in the anaerobic conditions in canned food.  Since C. botulinum also produces a lethal toxin, it is essential to destroy the spores.  So we heat the food in the cans to temperatures above boiling point (in fact we heat to the equivalent of 121.1C for 2.52 minutes and this is called a 12D process).  Properly processed LACF is safe.

When we look at acid foods, we find that C. botulinum is incapable of growth under these acid conditions and so no toxin can be produced.  Since we don't need to deliver a 12D process, we can heat for a shorter time or at lower temperature.  This has the advantage that the food is changed less and it costs less to deliver the process.  Depending on the food and the degree of acidity, we really need only destroy vegetative (i.e. non-sporulating) pathogens and spoilage microorganisms.  This will then destroy Listeria.

What about my conditional clause above?  If the food canner doesn't properly control the process, it might be possible for cans to be underprocessed.  This might occur if the steam supply to the retort (pressure cooker) is lacking or turned off too soon.  Another possibility is that cans might by-pass the retort altogether.

Post-processing contamination could occur if the cooling water is contaminated.  The can seals are not 100% watertight while they are still hot, so using contaminated water may allow a few bacteria to enter the can during cooling.  This resulted in a typhoid outbreak in Aberdeen in 1964, when people consumed imported Argentinian canned  corned beef that was cooled in untreated, sewage-contaminated river water.

Damage to the can seams caused by rough handling can also allow contamination, as there is a partial vacuum in the can.  Momentary opening of the seam caused by a blow can permit bacteria to be drawn into the can.

In summary, providing cans are properly processed and handled with reasonable care, LACF are essentially sterile, so all bacteria, including Listeria will have been killed; ACF are pasteurised and this process will also kill Listeria.

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.

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.

 

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.

More on Listeria contamination of vegetables

On 18th January 2011, I wrote about the withdrawal of salad vegetables from certain supermarkets in New Zealand because of possible contamination by Listeria  (See Listeria Hysteria).

 This week, I came across a paper published in Food Microbiology, describing the transfer of Listeria innocua from contaminated compost and irrigation water to lettuce leaves.  (M. Oliveira et al. Food Microbiology 28 (2011) 590-596).

These authors noted in their introduction that "Fresh produce can become contaminated at any point during the primary production, processing, distribution and preparation.  Primary sources of preharvest contamination include soil amended with untreated or improperly composted manure, contaminated irrigation water, the presence of wild and domestic animals, infected workers, and unclean containers and tools used in harvesting.  Research has demonstrated that many human pathogens are able to survive for extended periods in soils, manure and water."

Listeria monocytogenes causes Listeriosis, a rare but serious disease in humans, with an incidence of 2-3 cases per million of the total population in England and Wales.

In their experiments, Oliveira et al used an avirulent strain - Listeria innocua.  They transplanted lettuce seedlings into pots containing soil and contaminated compost;  compost manually surface irrigated with contaminated water after the seedlings were transplanted; and treated a third set of seedlings by hand-spraying contaminated irrigation water onto the lettuce leaves after transplanting.

These workers reported that the lettuce leaves became contaminated with Listeria from the soil and, not surprisingly, sprinkling with contaminated water also resulted in contamination of the leaves with Listeria, which survived for some days.  The bacteria survived in the compost for more than 9 weeks, giving ample opportunity for contamination of the leaves by transfer of soil.

Clearly, as these workers showed, irrigation water used for fresh salad vegetable growth must be pathogen free and manure used in compost must also be treated to remove pathogens.

Poor quality of reporting

I have just read a couple of articles in a national newspaper.  These report on the recall of bagged salads because of possible Listeria contamination and the death from avian botulism of wild birds in Auckland.

Listeria monocytogenes is a bacterium that causes a rare, but serious disease in humans.  (See Listeria hysteria).  The first article includes an information box, in which the symptoms are described as "a mild viral infection".  Bacteria are not viruses and the two entities are as different as lobsters and soft cheese!

The second article describes the increase in numbers of wild birds dying because the very warm water temperatures (up to 26C) have allowed rapid proliferation of Clostridium botulinum, which produces a neuroparalytic toxin.  The information box in this article claims that "the toxin thrives in still, shallow, warm water".  The toxin does not "grow or increase in bulk", though the bacterial cells that produce it may do.

Neither of these errors is likely to result in injury if the reader follows the advice in the articles, but it is just plain, sloppy reporting.  Google lists 1.16 million articles on L. monocytogenes and 541,000 on C. botulinum, so there is no excuse for the reporters' not having done a bit of background reading.  We all make mistakes in our writing, but if we set out to educate, then we really ought to check the simple details. 

I stand ready to get hammered if this blog contains stupid errors!

Avian botulism is caused by Type C toxin, which does not affect humans.

Listeria hysteria

Foodstuffs Own Brands in New Zealand has this weekend recalled baby spinach and various salad mixes because of possible contamination with Listeria.

The recall was reported in newspapers and picked up by TVNZ news and given a special segment in the evening Close Up current affairs programme.  Unfortunately, it was given the same sort of treatment as might befit a tsunami. 

In my opinion, Foodstuffs has done the right thing - they know that there is a problem with a product from their supplier and they have withdrawn it from the market to protect their consumers' health and their reputation.

But the presence of Listeria in salad vegetables is practically impossible to avoid.  The Microbiological Reference Criteria for Foods note that all foods produced by a process which is capable of achieving a Listeria-free product should test negative for L. monocytogenes in 5 samples of 25g.  (Reference Criteria are guidelines to indicate when food can be considered unacceptable or unsafe).  The criteria do not apply to raw fruits and vegetables, and bagged salad vegetables do not receive a listericidal process.

Where does L. monocytogenes come from?  The bacterium is widely distributed in the environment and can be found in decaying vegetation, soils, animal faeces, sewage, silage and water.  It is not surprising that salad vegetables will sometimes be contaminated from these sources.

Most bagged salad vegetables are given multiple washes, culminating in a chlorine rinse, which can reduce the levels of L. monocytogenes by a factor of about 10 (a 1 log reduction).  Provided that the numbers of L. monocytogenes are less than about 100/g at the point of consumption, they are unlikely to cause disease.  Many producers recommend re-washing at home before consumption.  However, it's difficult to dry the leaves and dressing doesn't stick to wet leaves, so it is likely that this recommendation is often ignored.  Refrigeration is also recommended, but it is probably better to take note of the 3-4 day shelf life, as Listeria can grow in the refrigerator, albeit slowly.  Growth is much less likely on dry, uncut surfaces.

The levels of L. monocytogenes required to cause disease are very difficult to assess and this is reflected in the varying compliance criteria adopted by different countries.  Listeriosis is a rare but serious disease in humans, despite frequent exposure to the causative organism, with an incidence of 2-3 cases per million of the total population in England and Wales.  Those most at risk are, in descending order, organ transplant patients, patients with AIDS or HIV, pregnant women and their unborn babies, cancer patients and the elderly.  New-born infants may also be infected from their mothers or other infants.  Non-pregnant healthy individuals are highly resistant to listeriosis.


What does this all mean?  Basically, if you look for Listeria in vegetables in the marketplace (and vegetables grown in your own garden) you will sometimes find it.  Various surveys suggest that the frequency of detection will be between 1 and 86%.  If a sample does test positive for Listeria, efforts should be made to find and eliminate the source of contamination.  The frequency of sampling should be increased and subsequent samples should test negative. 

There is no room for complacency, even in companies that have never had a positive Listeria test, but a single positive sample should be viewed with a modicum of restraint.

Time for red faces? Perhaps raw milk is not all it's cracked up to be.

The last time I wrote a blog on raw milk, I received "fan mail" accusing me of being sensationalist and closed minded.  At risk of more unflattering comments, here is another post on the subject.

Proponents of raw milk consumption have long claimed health benefits of raw milk and products made from it.  One of those claims is that lactose intolerant individuals, who don't produce sufficient lactase in the small intestine, suffer reduced symptoms if they consume raw milk, rather than pasteurised.   

Stanford School of Medicine recently conducted a study of self-reported lactose intolerant individuals, who were given raw milk, pasteurised milk and soy milk in a randomized, double-blind, three-way crossover trial. This classic experimental design removes bias in experimenters and subjects.  If lactose intolerant individuals consume lactose (the sugar found in milk) they cannot break it down to glucose and galactose.  Anaerobic bacteria in the colon grow on the lactose and produce hydrogen, some of which enters the bloodstream and appears in exhaled breath.

The participants were tested for exhaled hydrogen on the first and last days of each 8-day exposure period.  There was no statistically significant difference between consumption of raw or pasteurised milk, but soy milk resulted in much smaller amounts of breath hydrogen.  Similarly, the symptoms reported - flatulence, abdominal cramping and diarrhoea - were the same for both raw and pasteurised milk.

The researchers reported that the results from their work, collected under standardised, controlled conditions, did not support the claim that, with respect to lactose intolerance, raw milk has benefits over pasteurised milk.

Meanwhile, raw milk and raw milk products continue to be linked with outbreaks of Escherichia coli and Listeria diseases

http://www.marlerblog.com/legal-cases/e-coli-and-listeria-in-raw-milk-and-cheese---growth-sectors-at-marler-clark/