Information
What foodborne illness actually is
"Food poisoning" is not one illness. It is a category covering dozens of different germs, and they behave so differently that the only thing they reliably share is that you swallowed something you should not have.
The most useful thing to understand is that the gap between eating and feeling ill varies enormously — from half an hour to several weeks. That matters because almost everybody blames the last thing they ate, and the last thing you ate is often innocent. If your symptoms began four hours after a meal, that meal is a reasonable suspect. But if the cause were Listeria, which can take one to four weeks to appear, the meal responsible would be one you have long since stopped thinking about.
This is also why we ask for the date and time of your visit rather than just the restaurant name, and why we wait for a second, unconnected person before we tell anyone anything.
See a doctor if any of these apply
- Diarrhoea with blood in it
- Diarrhoea lasting more than three days
- A fever above 102°F (39°C)
- Vomiting so persistent that you cannot keep liquids down
- Signs of dehydration: passing little urine, a dry mouth and throat, or dizziness on standing
Some groups get seriously ill from infections that would barely trouble anyone else: adults over 65, children under 5, pregnant women, and anyone whose immune system is weakened by illness or treatment. If you are pregnant and have a fever with flu-like symptoms, contact your doctor straight away rather than waiting to see how it develops.
Filing a report here is not a substitute for medical care and does not reach anyone who can treat you.
The germs behind most cases
Listed by how quickly they tend to appear. Ranges are wide and they overlap heavily, so this cannot tell you which one you have — only a laboratory test can do that. It is here to show why timing matters, and why the meal you suspect may not be the one responsible.
Norovirus
Starts: 12 to 48 hours
Feels like: Vomiting, diarrhoea, nausea, stomach pain. Often comes on very suddenly.
Lasts: 1 to 3 days
Usually from: Produce, shellfish, and ready-to-eat food handled by someone who was already ill.
Salmonella
Starts: 6 hours to 6 days
Feels like: Diarrhoea, fever, stomach cramps, vomiting.
Lasts: 4 to 7 days
Usually from: Poultry, eggs, beef, vegetables, fruit, sprouts.
Campylobacter
Starts: 2 to 5 days
Feels like: Diarrhoea that may be bloody, cramps, fever, vomiting.
Lasts: About a week
Usually from: Chicken, raw milk, shellfish, turkey, contaminated water.
E. coli
Starts: 3 to 4 days typically, sometimes 1 to 10 days
Feels like: Severe stomach pain and diarrhoea that is often bloody, with vomiting.
Lasts: 5 to 10 days
Usually from: Undercooked ground beef, raw milk, soft cheeses made from raw milk, raw produce.
Clostridium perfringens
Starts: 6 to 24 hours
Feels like: Diarrhoea and stomach cramps, usually with no fever and no vomiting.
Lasts: Under 24 hours
Usually from: Beef, poultry and gravies held too long at the wrong temperature — a classic buffet and catering problem.
Staphylococcus aureus
Starts: 30 minutes to 8 hours
Feels like: Nausea, vomiting and cramps that begin abruptly.
Lasts: About a day
Usually from: Sliced meats, sandwiches, pastries and puddings handled after cooking.
Bacillus cereus
Starts: 30 minutes to 6 hours if it causes vomiting, 6 to 15 hours if it causes diarrhoea
Feels like: Either sudden nausea and vomiting, or watery diarrhoea and cramps.
Lasts: About 24 hours
Usually from: Rice, leftovers, sauces and soups left standing at room temperature.
Vibrio
Starts: 2 to 48 hours
Feels like: Diarrhoea, vomiting, abdominal pain. Severe cases can involve shock and skin lesions.
Lasts: About 3 days
Usually from: Raw or undercooked oysters and other shellfish.
Shigella
Starts: 1 to 7 days, usually 1 to 2
Feels like: Sudden cramping, fever, and diarrhoea that may be bloody.
Lasts: 5 to 7 days
Usually from: Food or water handled by someone who is ill. Spreads easily person to person.
Listeria
Starts: Usually 1 to 4 weeks, occasionally as long as 70 days
Feels like: Fever and diarrhoea. Serious cases involve stiff neck, confusion or convulsions.
Lasts: Days to weeks
Usually from: Deli meats, smoked seafood, soft cheeses, raw milk, raw sprouts.
Hepatitis A
Starts: 15 to 50 days, around 28 on average
Feels like: Fatigue, fever, diarrhoea, dark urine, pale stools, yellowing of the skin or eyes.
Lasts: Usually under 2 months, occasionally up to 6
Usually from: Raw shellfish, raw produce, contaminated water, or an infected food handler.
Where these figures come from
Onset times, symptoms, durations and food sources are taken from FoodSafety.gov, the joint HHS, USDA and FDA consumer site, and the guidance on when to seek care is from the CDC. We have not adjusted any of it. Neither agency is connected with this service.
This page is general information, not medical advice, and it is not a diagnosis. If you are unwell, speak to a doctor.