The bacteria

We've used the term "bacteria" to refer to the micro-organisms that grow on food and can infect anyone who eats it. Strictly speaking, these harmful bacteria are known as "pathogens". Many other bacteria are harmless.

We have also adopted the widely used term "food poisoning" to mean food-related illness. The correct term is "foodborne illness": it covers the whole range of illnesses that can be passed on through food, some of which can cause problems many days after contact. Technically, "food poisoning" only occurs when bacteria have produced toxins which cause diarrhoea and vomiting soon after eating the food.

Campylobacter is the most common cause of foodborne illness in New Zealand. Just one drop of contaminated chicken juice can make you very sick.

Common symptoms include stomach cramps, nausea, diarrhoea (sometimes with blood) and fever. More serious effects are possible. It can strike up to 10 days after you eat the contaminated food, and the effects will probably last for several miserable days.

Salmonella is the next biggest threat. It usually strikes within 12 to 36 hours of your eating the contaminated food, and has similar symptoms to campylobacter (but without blood in the diarrhoea). You'll feel really awful for a couple of days, and may not fully recover for weeks.

E. coli (variant O157:H7), also called VTEC, is a bacteria carried in the gut and manure of cows. During slaughter, it can get onto the outside of the meat. If the meat is minced, and the mince is not well cooked, it can pose a serious risk of kidney problems, especially to the very young, the elderly and others with weak immune systems.

E. coli O157 is not widespread in New Zealand yet, but in the US there have been many reports of E. coli illness caused by undercooked hamburgers. It has also been found in unpasteurised milk.

In the worst cases, the illnesses caused by all these bacteria can kill.