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.