Friday, November 17, 2006

Should I eat the chicken?

A recent publication in New Zealand caused a lot of interest by claiming that sale of raw chicken should be banned, in favour of frozen chicken. The basis for the claim was that chicken meat is routinely contaminated with Campylobacter. The freezing process would kill the Campylobacter and render the meat safe.

Was this claim justified?

First we need to understand something about chicken farming, chicken processing and, not least, Campylobacter.

Let's start with Campylobacter. Campylobacter is a bacterium commonly found in animals and the environment. It can get into food via many different contamination vectors (carriers), including untreated water, birds, insects and animals. It is often found in the farm environment, which may be contaminated by animals.

The number of Campylobacter we need to eat to become infected is very low; various estimates put the "infecting dose" at between 6 and 800 cells. This means that even low levels of contamination in food can cause a disease if the food is consumed. Even contact with infected animals, for example in petting zoos, can put sufficient bacteria onto the fingers to give an infecting dose if they are put into the mouth (a problem with little children) or used to prepare food without first washing them carefully.

"But surely" you are asking "we cook chicken before we eat it". Well, yes we do. Assuming that we cook it properly, the Campylobacter cells will be killed and the chicken is safe to eat. But supposing that we handle the raw chicken and then prepare a salad; or we use the same chopping board to prepare the raw meat and then cut the salad on the same board, using the same knife? If we don't wash and sanitize the knife and board, we can "cross contaminate" the food from the chicken, via the knife and board.

The suggestion that raw chicken should be banned, and only frozen chicken sold now has some attraction. "Freezing kills Campylobacter, so that will make the chicken safe and we won't get cross contamination, right?" Well, it goes some way to reducing the contamination. But, as with most things to do with bacteria, it's not black and white. Again, estimates vary; freezing may destroy tens of millions of Campylobacter, but equally may have little effect. FAO/WHO data suggest a hundred-fold reduction if the product is frozen and held for a minimum of 3 weeks. A reduction of a hundred-fold sounds a lot, but in microbiological terms this might still leave millions of bacteria on the product. And as we have seen, this is plenty to give an infecting dose.

So, to go back to the title of this posting, should we eat the chicken? My personal opinion is a qualified "Yes". The caveat is that we must make sure to handle the raw chicken safely, preventing cross contamination of utensils, surfaces and other foods in the kitchen. Cook the meat properly and prevent recontamination.

The New Zealand Food Safety Authority (NZFSA) says that two of the most important ways of keeping food safe are to follow the 4Cs rule – Clean, Cook, Cover and Chill the food. Also follow the 20+20 hand wash rule before and after handling poultry and preparing food - wash your hands, using plenty of soap and warm water for at least 20 seconds, paying careful attention to finger nails and the webs between fingers. Rinse well and dry them for a further 20 seconds, using a clean dry hand towel or disposable paper towel. It has been shown that wet hands can transfer microbial contamination to utensils, refrigerator door handles, taps and other potential cross contamination points, so the drying is just as important as the washing.

Odd Spot: On 3 December 1988, Edwina Currie, the outspoken junior health minister in the UK Thatcher government was quoted as telling ITN, "Most of the egg production in this country sadly is now infected with salmonella." Sales of eggs plummeted 60 per cent overnight. The loss of revenue forced farmers to slaughter four million hens and 400 million unsaleable eggs had to be destroyed. The government had to provide a multi million pound rescue package for the poultry industry and the unfortunate Ms. Currie resigned on the 17th December. Undoubtedly, there was some substance to her claims. Vaccination of hens to protect against salmonella has now greatly reduced the levels of egg contamination to the present 0.3% reported by the latest FSA survey and since 1997 the incidence of salmonellosis in UK has fallen by a factor of about 4x. However, there is still a concern that eggs on sale in UK may contain Salmonella Enteritidis organisms, perhaps as a result of importation of eggs produced by unvaccinated hens.

Perhaps Edwina was right. Only time will tell if the advocates of frozen chicken are right too.


Anonymous said...



Anonymous said...

Thank you very much for sharing your knowledge with the public because, as we know, the public school system has historically failed to offer enough education to ensure a healthy life. You've done an outstanding job of clarifying muddled messages we get from the varied sources.

Mark said...

This article was very interesting, and I was wondering if you had any thoughts on the raw food diet for dogs? (We currently advise our customers not to feed their dog raw food because of the risk of bacterial infection from campylobacter, etc.)

John said...

Thanks for your comment, Mark. I'm not a veterinarian, so my comments are based on observation.

If any domestic pet becomes infected with an enteric organism, there is some risk to the owners and children. If they handle the animal and then eat without washing their hands, they run the risk of infection themselves.

In terms of risk to the dog, I don't think that feeding raw food is a major issue, provided that the meat is of good quality. Obviously, there is some risk if the meat is feral, but most owners would not be shooting or trapping wild animals to feed to their pets. I had two farm dogs and you really would not want to know what they found and ate on occasions! Dogs seem to have a much more robust digestive system than we weak humans.

I emphasise - these are my personal observations, rather than professional opinion.

FunTimeKiller Blog said...

This blog is a fantastic resource to get educative information! Will you be mind if I make a trackback of a couple of of your blog posts on my own website?

John Brooks said...

FunTimeKiller: you are welcome to link to these posts.

Yakout Esmat said...

I recently discovered this website and after going through few of the posts i can say that this is an excellent source of information to the public who are interested to learn about food safety and what goes on sometimes in the industry. Have few questions about chicken and eating safety:
1- what is the temperature to which when chicken has reached during cooking it is considered safe to eat?
2- what temperature and time duration can a commercial kitchen keep cooked chicken "holding" before they either sell it or or get rid of it?


John Brooks said...

Chicken should be heated to 75C to ensure that all vegetative pathogen cells are killed. Remember that this includes any stuffing, which slows down the rate of heating of the whole bird.

Foods displayed hot must be held above 60C and preferably for less than 90 minutes. Holding should not be longer than 2 hours in aggregate.

lucia said...

How about using raw eggs to make ice cream which is then frozen? Is there still a risk of infection?

John Brooks said...

Lucia: See my post on this subject:

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