Food poisoning is any disease caused by eating infected or contaminated food. Normally this is a bacterium or virus causing gastroenteritis. The exact symptoms vary according to the pathogen, but commonly include stomach cramps, diarrhoea and vomiting.

Cases of food poisoning are extremely common, but most go unreported or even unnoticed by the sufferer. Estimates on the number vary wildly, with figures around 25 million cases per year in the US and 2 million per year in the UK being quoted. Of these, the commonest bacterium is campylobacter jejuni. This was only isolated in 1971 and isn't widely known by the general public, but is now known to cause the majority of food poisoning incidents. Other less common, but better known, bacteria are salmonella and escherichia coli (E. coli).


There is a lot of misinformation and press hype around all aspects of food safety. There a few simple precautions that can be taken to minimise the risk of infection. The mother of a friend of mine has the worst practices I've ever seen, so I'll use her examples. Let's call her L. It's a wonder she's still alive. She must have an industrial-strength immune system.

  • Avoid cross contamination
    If you have something that will not be cooked further, or eaten raw, it is imperative that you don't let it come into contact with contaminants. Use different knives, chopping boards and other utensils, or wash them thoroughly between use. One of the most terrifying food crimes I saw was when L took chicken out of the dish in which it had been marinading, barbequed it, then returned it to the same pan. It was then able to soak in the lovely salmonella juices, while nicely warmed to a cosy temperature for the bacteria to breed. Hygiene is important of course. If someone if cooking for you, make sure they wash their hands!
  • Cook food thoroughly
    Certain foods, particularly meat, are extremely likely to be infected with bacteria. Chicken and eggs from large scale factory farms are bad offenders. Care should be taken with these risk foods to cook them long enough so that every part of them rises about 65°C. This is the temperature at which protein denatures, so most bacteria will be killed. If making tasty raw beef dishes like carpaccio or steak tartare, you should sear the meat on the outside before using it. L's bloody chicken is legendary.
  • Keep hot food hot and cold food cold
    I said above that most bacteria are killed by proper cooking. Be careful though: some bacteria are spore-forming. When they detect hostile conditions they form spores that can survive until conditions are more favourable. Once this happens, they can then germinate and breed again. If your food will stay hot, then it's not a problem, as they never get a chance to breed again, but if it to be served cold, care must be taken to chill it quickly so that there is never time for the spores to germinate. If food low in acid is to be bottled or otherwise preserved without refrigeration, it needs to have a high-temparature botulinum cook to destroy the spores themselves. L likes to cook rice dishes that then remain at room temperature as the bacillus cereus spreads through their protein-rich goodness. Hot food should be kept above 70° and cold below 7° C.

There are more things that are important, such as avoiding reheating food more than once, but those above are the most important and commonly missed.

The bugs

While there are some exceptions, such as the Norwalk Virus and some mould, most food poisoning is from bacteria. These are some of the most common or most dangerous. All of this is from my perspective of the UK, but it is a similar situation across most first world countries. Many of these have good writeups of their own. I'll just provide a short description of each.

  • Campylobacter jejuni
    This is the commonest cause of food poisoning, despite not being widely known to the public. It is commonly found in the guts of humans and animals, and is therefore usually transmitted by simple cross contamination. It can also be found in contaminated drinking water. Symptoms include diarrhea, abdominal cramps, nausea and fever, but there can sometimes be more serious complications. See BlueDragon's writeup for more detail.
  • Salmonella
    A very well known group of bacteria. Infection is very easy, as as few as 15 cells may be enough to cause it. Poultry and eggs are the commonest source, and it is prudent to assume that all chickens are infected. It has been found in the yolk of eggs, so unless you want to eat all your eggs cooked hard, make sure you buy good free range eggs and eat them while very fresh. A case of Salmonella poisoning usually lasts for a few days, but in some cases can continue for many weeks. Bacteria may remain present in the body long after that. Symptoms include the usual diarrhea and abdominal pain associated with gastroenteritis. The symptoms can also cause dehydration. Complications can occur, and deaths often happen among high risk groups such as the very yound and old. Those with weak immune systems, such as people with AIDS, often become infected with Salmonella and suffer serious complications.
  • Staphylococcus aureus
    Very commonly found in the environment, and also carried by human and animal hosts without illness. It lives in the noses, mouth and on the skin and hair of humans. This is why hygiene is so important! Wash your hands after smoking, as bacteria can be transferred from your mouth to hands. As ilness from Staph is not usually serious, it is thought that the vast majority of cases go unreported, with many food workers probably infected. Symptoms include nausea, diarrhea and vomiting.
  • Clostridium botulinum
    While luckily not common, Clostridium botulinum is probably the most serious food poisoning bacterium. Found mainly in soil, the bacterium is spore-forming and anaerobic. This means that most infections come from badly processed preserved food where the spores survive the bottling process and thrive in the airless environment. As the bacteria multiply, they produce botulinum toxin, a powerful neurotoxin or nerve poison. This is the most potent natural toxin known to man. It causes botulism, sypmtoms of which include dizziness, disorientation, difficulty in breathing and swallowing, paralysis and often death. Careful with those canned meats and mushrooms!
  • Listeria monocytogenes
    Infection with listeria usually causes no symptoms, but two unusual feature of this bacterium make it worth remembering. Firstly it can cross the placenta and infect the fetus. The other usual feature of it is that it can multiply at temperatures as low as 3°C. This means that refrigeration doesn't help. For these reasons, pregnant women should avoid unpasteurised milk and cheese. In the US, all cheese must be pasteurised anyway, even though listeria does not cause any problems for those who are not pregnant or with weak immune systems.
  • Bacillus cereus
    A spore-forming bacterium, found in dry foods such as rice, pasta and dried herbs and spices. The spores can survive in the dry and dormant state for extremely long periods, and can then also survive regular cooking. For this reason always refrigerate cooked rice and similar if you're not eating it while still hot. There are two forms of the toxin that B. cereus produces. They cause syptoms at different stages of the digestive process. One causes nausea and vomiting, while the other diarrhea and abmdominal cramps.
  • Escherichia coli
    This bacterium has been getting a lot of press recently, with several well-publicised outbreaks in the US and UK. E. coli is found almost everywhere. It is found in all human guts as part of the friendly intestinal flora as well as being ubiquitous in the wider environment. It rarely causes any problems. The strain that causes all the trouble though, is not so benign. Escherichia coli O157:H7 is a rare enterohemorrhagic strain of E. coli. This means it causes bleeding in the colon. It has up to a 50% fatality rate among the very old and very young, and is a serious concern.
Other pathogens, that I may expand upon at a later date, include:

OK, has that scared you? Don't be too afraid, just take some of the simple precuations I've given above. I studied this for months at college, and I still eat raw eggs and shellfish with wild abandon, but I guess I'm young and foolish. Eat safely.

The FDA Bad Bug Book:
The E. Coli Index -
Annette Abbott, my old food science lecturer, who got me through my CIEH Intermediate Food Hygiene Certificate with flying colours.

The day that Princess Diana died I went to a Filipino picnic in Toronto to celebrate the first birthday of the son of an acquaintance of mine. The kid, Xavier, was just a little drooly thing who had no idea what it was all about, but everyone else was keen for a party, Philippines style. I was the only white person there, which didn't bother me at all, as I have spent substantial periods of my life surrounded by people of other skin hues speaking languages I don't understand. What did unsettle me was the pig. I've since discovered that a whole pig is de rigueur at a Filipino picnic or celebration of any sort, and this one was no exception. The pig had been cooking all night in preparation for this shindig.

Pride of place on the main table was yielded to the carcass of the barbecued pig itself, head (no fruit in mouth, disappointingly), feet, and tail prominently displayed in case we might think they had skimped and only served half, or three quarters of a pig. You could carve a hunk of roast pork off this baby, and then choose from a host of pig-related items as accompaniments: pork crackling salad, pork slices, pork fat, cracked pig leg bones filled with marrow...It was a pig fest, for sure. Lucky thing I'm not a vegetarian.

I've got a strong stomach, but an hour or so after polishing off my second plate of pig-related food items I started to feel a bit bloated. I just thought I ate too much. But by the evening I was feeling very strange indeed, feverish and dizzy. Unable to do much, I turned on the TV, and all that was on was Di Di Di, on every channel. I lay shivering on the bed and stupidly watched the coverage, bolting to the bathroom frequently while I ate bananas and drank tea to try and calm my stomach. Luckily this was a very mild bout of pork poisoning, and by the time the news stories wound up to repeat their babble for the fifth time, I was feeling much better.

Though not as dramatic as the time I repeatedly projectile vomitted all over the train tracks in Bangkok, or the time in Chiang Mai that I evacuated so much that my shit was totally clear and odourless, this experience was nonetheless memorable. Now, the death of Diana, the barbecuing of a whole pig, and food poisoning are inextricably intertwined in my mind.

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