Is hamburger a greater risk for E. coli?

The subject of coliforms in food and specifically the question about hamburger comes up often in the referrals to this blog.

Coliforms are used in the food industry as indicators of general hygiene. This sounds simple, but it is not quite straightforward; we need to understand what coliforms are and how they are measured before we can draw conclusions.

The term “coliform” does not refer to a unique species. In fact, coliforms are a group of bacteria defined by the test used to detect them. Thus, we can carry out a simple culture test that will count or show the presence or absence of this group. Each country uses slightly different tests. One protocol defines coliforms as:

“Gram negative rods that produce acid and gas from lactose in the presence of bile salts at 37 C in 24 to 48 hours”

Notice that there is no mention of genus or species or connection with faecal contamination. In fact, the group includes several genera that are capable of growing in the environment and have no faecal connotation, so finding coliforms on lettuces should not be cause for undue concern. What we can say is that all of these bacteria should be killed by pasteurization temperatures, so if they are found in pasteurized foods, the hygiene of the process has been poor.

If we want to show that faecal contamination of food has occurred, we do a test for Escherichia coli, which is found at high concentration in faeces. This test for “faecal coliforms” was originally used to test water, where the organism cannot grow. The situation in food is a little more complicated because the organisms may grow in the food, but the finding of E. coli in food is good evidence of faecal contamination. Properly pasteurized food should not contain any faecal coliforms. Raw foods, such as leafy vegetables, can become contaminated by faecal coliforms if birds or animals have access to the crops. This was the probable cause of E. coli O157:H7 contamination of raw spinach last year.

Meat animals all have E. coli in their intestines and there is a possibility of contamination of the carcase by spillage of gut contents during slaughtering. This contamination will initially be on the meat surface, but will be distributed throughout the meat if it is minced or ground. This is why steak can be eaten “rare”, since the interior of meat from healthy animals is sterile – all that is required is for the exterior to be cooked to a temperature of about 70 – 75 C. However, hamburger patties are made from ground meat and must therefore be cooked right through to ensure destruction of faecal bacteria that may have been mixed in. Americans tend to eat hamburger cooked less thoroughly than in other countries. The USDA suggests 71.1 C (160 F) for beef burgers. So the real issue is not that hamburgers are at greater risk of contamination, but that undercooking them may allow E. coli to survive.
See Guaranteed safe At what cost (?) October 17, 2007
http://foodsafetywithjaybee.blogspot.com/2007/10/
guaranteed-safe-at-what-cost.html

What interests you most?

My Sitemeter collects statistics on usage of this blog (don’t worry, you can’t be identified) including pages visited and referrals from search engines like Google and Yahoo.

I looked through some recent stats and found that the most common questions referred to the safety of chicken (by far the most frequent referral), unpasteurized milk, coliforms and how bacteria can get into food. There were one or two surprising enquiries, but I won’t go into those.

Over the next few posts I’ll visit some of the more popular questions, starting with a report from New Zealand on campylobacteriosis and poultry.

The March 2008 Monthly Surveillance Report from ESR makes for interesting reading. http://www.surv.esr.cri.nz/surveillance/monthly_surveillance.php?
we_objectID=1548

The incidence of campylobacteriosis in the human population of New Zealand has fallen again. 450 campylobacteriosis cases were notified in March 2008 compared with 1145 cases notified in the same month of the previous year. The current 12 month rate* is 234 cases per 100,000 head of population, compared with 386 for the previous 12 months to March 2007 – a 39% reduction. Compared with the rates of other infectious diseases surveyed, this is a very significant achievement.

Though there is currently no direct evidence, at least some of this reduction must be because of the strenuous efforts made by the poultry industry to reduce the levels of contamination on fresh poultry and poultry products.

The Campylobacter surveillance data contain other interesting observations on the possible source of infection: of the cases where the information was recorded, 51% had eaten food from a food premise (I assume that means a restaurant or take-away); 38% had contact with farm animals; 22% had contact with other people showing symptoms of campylobacteriosis. Other possible links included pre-schools and childcare, drinking non-habitual or untreated water supply or contact with recreational water. A surprising 17% reported faecal contact, while a small proportion reported contact with a sick animal.

Obviously, this information is confounded and incomplete and doesn’t explain exactly how the patients contracted campylobacteriosis. However, it does point to the special nature of life in New Zealand and suggests that we need to look widely to find ways to control our high incidence of campylobacteriosis.

(For further information on Campylobacter, either select "search blog" using the keyword Campylobacter, or go to "So what is this Campylobacter thing?" posted Tuesday 21st November 2006 by clicking the Archive).

How do you know chicken is safe to eat? If you cook it yourself, use a meat thermometer to check the internal temperature reaches 74 C (165 F). The USDA suggests 160 F (71.1 C) for beef burgers. If you buy chicken ready-cooked for reheating, use the same temperatures. If you are going to eat pre-cooked chicken without further heating, make sure you trust the supplier.


* The 12 month rate is based on the cumulative total for the current year (12 months up to and including March 2008), expressed as cases per 100,000

The news just keeps on getting worse!

After so many years of living with a food microbiologist, my wife has become a valuable food retail spy. Today she told me two more horror stories:

In our local supermarket there is a display stand for unwrapped bakery goods that extends from about chest height down to the floor. The store manager has supplied tongs for customers to use and there are signs asking customers to use the tongs.

Today she arrived at the bakery counter in time to see a mother wrestling the tongs from her toddler. If this were not bad enough, the mother then said to the toddler “I thought you said you were going to eat that”. Grabbing a bun from the child’s other hand, she stuck it back in the cabinet. Now both of them had handled the bun.

Now, I realise that bread buns are not a particularly good growth medium for food poisoning bacteria, but this is unacceptable. Some food borne pathogens have a very low infecting dose. The display cabinet should be arranged so that products and tongs are inaccessible to toddlers. Owners of self-service food displays need to be aware that simply providing tongs does not guarantee the safety of the food they sell. Needless to say, we will not purchase unwrapped goods from that store again.

The second incident was observed on TVNZ’s Good Morning show. Unfortunately, I didn’t see it and have not been able to locate a replay on their website. It appears that The Mad Butcher was on the show and demonstrating the preparation of chicken. After handling the raw chicken, he put his fingers into some spices and tasted a pinch. The bowl of spices was thus contaminated with whatever bacteria were on the raw chicken. A short while later, he put a cooked chicken onto the same chopping board, contaminating it with raw poultry juices.

OK – the Mad Butcher is not a professional chef and neither is Steve Grey, the host for that segment. The poultry industry in New Zealand has had a bad press recently over Campylobacter food poisoning, allegedly transmitted largely via chicken (though in fact we have seen a significant and sustained reduction over the last year in the incidence of the disease in the human population). This sort of example on daytime television, which is probably watched by many young mothers, is perhaps one of the reasons that we see such a high incidence of campylobacteriosis in New Zealand. Young adults are not getting the food safety message and we need to have good kitchen habits shown on our national television channels. We can’t rely on the food suppliers to take total responsibility for control of food poisoning.

This type of poor kitchen practice is not confined to New Zealand; Doug Powell at Kansas State University, who runs the Food Safety Net and writes the Barfblog has castigated some TV chefs in the USA for similar indiscretions (see for example: http://barfblog.foodsafety.ksu.edu/tags/tv/).

Pigeon pie, anyone?

What does it take to make us clean up our act?

Having lived in Hong Kong for a while, I am perhaps more aware of the potential for the spread of diseases than the average Kiwi. The Chinese have suffered SARS and bird flu and are very keen to avoid more outbreaks of either. If you sneeze in public, people will stare accusingly at you; people who have a cold will voluntarily wear a face mask out of consideration for others; there are hand sanitizing stations around public buildings and patrons are warned not to feed birds in outdoor eating areas.

With these thoughts in mind, I have been surprised to see the couldn’t care less attitude of some businesses here at home. When a fly crawling over the goods in a bakery was pointed out to the assistant, she shrugged her shoulders and said that it was impossible to keep them out. There is a coffee and cake shop on the podium level of the apartment block where I live. They have a resident population of flies there too. But in addition, they have birds. Not in cages as decoration, but possibly as employees. These birds hop around on the floor and pick up crumbs. They also hop onto the tables on the terrace and finish off the meals left by the patrons – the plates stay on the tables long after the diners have left. This is just not acceptable in any food service premises.

New Zealand has been lucky and so far avoided bird flu scares. However, bird flu is not the only concern. When birds hop around on floors or tables and perch on chairs, they are inclined to leave droppings behind. If eventually an assistant comes to remove the plates, the table will be wiped with a cloth, spreading a thin film of droppings around and probably contaminating the whole surface with faecal bacteria and viruses. Of course, we don’t eat off the table, but it would be hard not to touch it and so there is a risk of ingesting these organisms, particularly if we eat cakes or breads with our fingers.

I would have expected these failings to be brought to the attention of the shop owners by the authorities. Perhaps we also put too much faith in antibacterial sprays. Are they an extension of the plastic glove = bullet-proof syndrome? We need to see safety in practice, not just in a manual on the manager’s shelf. I hope it will not take a SARS epidemic or outbreak of bird flu to convince these businesses to clean up their act.

Campylobacter jejuni - SEM image

Scanning electron microscope image of Campylobacter jejuni, illustrating its corkscrew appearance and bipolar flagella. Source: Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, Virginia.

That Campylobacter problem – it just doesn’t go away

It has been fascinating to watch the news reports, both here in New Zealand and overseas, over the last few weeks and see the different takes. The New Zealand Food Safety Authority announced on 15th January the introduction of a Code of Practice for the poultry industry. The code is intended to reduce the incidence of campylobacteriosis in New Zealand, which is the highest in the developed world. The code has received mixed reviews and the language used has at times been intemperate. The blame for much of this disease has been laid at the door of the poultry industry as suppliers of “New Zealand’s cheap and dirty food”. In a Radio NZ interview, Dr. Mike Baker claimed that when chicken is prepared in a kitchen, every surface in the kitchen will be covered with bacteria and the aprons of workers in restaurant kitchens will potentially be covered in a layer of Campylobacter.

When interviewed by the Taranaki Daily News, a Tegel spokesman said that the Company fully supported the new code. Sharon Wagener of NZFSA says that the code formalises a lot of what was already happening voluntarily in the industry. However, on the Green Party website their spokesman Sue Kedgley claimed that the code “fails to include some very simple measures to stem the tide of Campylobacter contamination of chicken meat being sold to New Zealanders”. Some of the points raised by Ms. Kedgley in relation to problems of mechanical handling and leaky packaging are not in dispute, but are already being addressed by the industry.

The Taranaki Medical Officer of Health, Richard Hoskins, noted that the Health Board has had interactions with Tegel (which of course is not the only chicken processor in the country) in efforts to reduce the incidence of the disease. He apparently expressed the view that the Board was "pretty impressed with the efforts they are going to".

Michael Brooks, the Executive Director of the Poultry Industry Association of New Zealand, has also stated that based on figures collected by ESR, human campylobacteriosis case rates have been steadily declining since August 2006, in some months showing a drop of 30-35% over the corresponding previous year. Of course, this does not satisfy everyone; the incidence of campylobacteriosis tends to be somewhat variable from month to month and it will require proper statistical analysis over some years to demonstrate a true decrease.

The adversarial approach being taken by some of the interested parties is not, in my view, the best way forward. Nobody has the complete right answer; where has the still small voice of reason and collaboration gone? Wouldn’t it be better if the parties worked together, using scientifically demonstrable facts and not overheated opinion to put together the jigsaw puzzle and solve the problem?

The fact is that human infection by Campylobacter is a very complex problem and simply pointing the finger at the poultry industry will not solve it, no matter what codes of practice are imposed. Take just one point: sub-typing of Campylobacter, using molecular methods, can show the relatedness of various isolates from poultry and from humans. In some parts of the country, a single sub-type is found in up to 20% of human cases and in poultry. In other parts, the sub-typing shows that human cases do not share the same types as found in poultry. Nobody is claiming that poultry does not contribute significantly to campylobacteriosis in New Zealand, but the industry takes this seriously and is doing something about it, having issued its own Broiler Growing Biosecurity Manual in consultation with NZFSA in August 2007. This describes the minimum standards to be used in NZ broiler production systems, aiming at ensuring the products meet food safety and suitability requirements and consumer needs. Campylobacter is a commensal bacterium – it is found in poultry and some other animals and does not cause them to be ill, so getting rid of it is going to require considerable effort and some cost on the part of farmers and processors.

The code comes into force on the first of March 2008.

For more information on Campylobacter, click here