Key pathogens and how to control them

You do not need to memorise every detail, but you should know which pathogen matters for which food. The onset times below are typical and vary from person to person. They help investigators, which is one reason why good records of what was served, and when, are so useful.

Salmonella is found in raw or undercooked meat and poultry, raw eggs and dairy products. Symptoms include diarrhoea, stomach cramps, fever and vomiting. They usually start 12 to 48 hours after eating and last 4 to 7 days. Control it by cooking food thoroughly and keeping raw food apart from ready-to-eat food.

Campylobacter is the most common bacterial cause of food poisoning in the UK. Poultry is the main source. It cannot multiply outside an animal or person, so it does not grow in food. Instead, small numbers on hands, boards or cloths are enough to cause illness. Symptoms usually start after 2 to 5 days. Cross-contamination is the main risk. Never wash raw chicken, because the splashes spread bacteria.

E. coli O157 lives in the gut of cattle and other animals. It can get onto raw meat, especially minced beef, and onto vegetables through soil. Fewer than 10 bacteria can cause infection. It survives chilling and freezing, and it tolerates acid, salt and dry conditions. Symptoms usually start after 2 to 4 days and can include bloody diarrhoea. About 1 in 10 cases develop haemolytic uraemic syndrome, which can cause kidney failure. Children under 5 are at greatest risk. Some people are left with permanent kidney or brain damage, and the infection can kill. A later module covers the controls.

Listeria monocytogenes is unusual because it can grow at chill temperatures. The risk comes from ready-to-eat chilled food, such as soft cheese, pâté, cold-smoked fish and cooked sliced meats. Illness can appear up to 70 days after eating, which makes outbreaks hard to trace. It is especially dangerous in pregnancy, where it can cause miscarriage or stillbirth, and for older people and those with weak immune systems. Control it with strict use-by dates, chilling at 5°C or below, good cleaning of chillers and slicers, and stock rotation.

Clostridium perfringens forms spores that survive cooking. It causes illness when large meat dishes, stews or gravies are cooled slowly or kept warm. It grows well between 15°C and 50°C. Symptoms are watery diarrhoea and stomach pain, usually 8 to 18 hours after eating. Most people recover within 24 hours. Control it by cooking in smaller batches, cooling quickly and keeping hot food above 63°C.

Bacillus cereus also forms spores and is closely linked with cooked rice. It can cause two kinds of illness. One causes vomiting, usually within 1 to 6 hours, and comes from a heat-stable toxin. The other causes diarrhoea after 6 to 24 hours. Control it by cooking rice in small batches, then serving it at once or cooling it quickly and chilling it. Do not leave cooked rice at room temperature.

Staphylococcus aureus lives on human skin and in noses and throats. It gets into food from hands, cuts and spots. If that food is then left warm, the bacteria produce a toxin. Symptoms start quickly, often within a few hours, with vomiting and stomach pain. Cold cooked meats and poultry are typical foods. Control it by handling food as little as possible, covering cuts, keeping staff with infected skin away from food, and keeping food chilled.

Clostridium botulinum is rare but life-threatening. It forms spores, grows without oxygen and makes a very dangerous toxin. Risk foods include under-processed preserved foods and chilled foods in vacuum or modified atmosphere packs. FSA guidance says that such chilled packs stored between 3°C and 8°C should have a maximum shelf life of 10 days, unless other proven controls are in place. Re-wrapping does not restart the 10 days. If you vacuum pack food, follow this guidance before you set a date.

Norovirus is a virus, not a bacterium. It is the most common cause of gastroenteritis in the UK. It does not grow in food, but a very small amount causes illness. It spreads from person to person, through vomit and unwashed hands, on surfaces, and through foods such as oysters and frozen berries. It survives freezing. Symptoms usually start 12 to 62 hours after exposure, with sudden nausea, vomiting and diarrhoea. Control it by keeping ill staff away, washing hands well and disinfecting thoroughly after any vomiting.

Hepatitis A is another virus that can pass into food from an infected person. It takes about 28 days on average for symptoms to start, and it can cause jaundice. This is one reason why food handlers must report jaundice.

Notice the pattern. Some pathogens must multiply in food before they cause harm, so time and temperature are the main controls. Others, such as Campylobacter, E. coli O157 and norovirus, cause illness in very small numbers, so the main control is to keep them out of ready-to-eat food.