Whenever anyone gets sick with a foodborne illness, the question is what food made them sick. Did the last thing you ate give you food poisoning?

The answer, surprisingly, is probably not. Bacteria that cause food poisoning have incubation periods. During that time, the bacteria grows and some produce toxins and your immune system starts to respond. The response is what causes the symptoms. It can take some time for the symptoms of food poisoning to develop, depending on the pathogen.

These incubation times are one reason why tracking the source of a food poisoning outbreak can be so difficult. First, investigators must interview patients and ask them what they ate in the past week. And second, it’s difficult for patients to remember what they ate in the past week.
These are the typical incubation periods for foodborne illness:

E. coli: 1 to 8 days
Salmonella: 6 to 72 hours
Campylobacter: 2 to 7 days
Listeria monocytogenes: 3 to 70 days
Brucella: 5 to 50 days
Vibrio: 1 to 7 days
Clostridium botulinum: 12 to 72 hours
Norovirus: 12 to 48 hours
Shigella: 4 to 7 days
Staphylococcus aureus: 1 to 6 hours
Bacillus cereus: 10 to 16 hours
Clostridium perfringens: 8 to 16 hours
Cryptosporidium: 2 to 10 days

These numbers are useful to investigators when they are trying to narrow down the specific pathogen that caused the illness. The average time of symptom onset is usually somewher in the middle of the typical incubation period.

The best way to diagnosis a foodborne illness is laboratory /confirm/iation, usually from a stool sample. Finding the pathogen in the stool is proof positive that that patient has listeriosis, or salmonellosis. Sometimes blood tests are performed as well. Doctors will also diagnose base on symptoms. For instance, bloody diarrhea is the classic symptoms of a Shiga toxin-producing E. coli infection, but it may also be a symptom of salmonellosis.

If a cluster of patients present with the same symptoms that indicate foodborne illness, an outbreak may be declared. Finding other patients with the same illness can also aid investigators who are trying to pinpoint the pathogen.

To protect yourself against food poisoning, and to get help quickly if you do get sick, it’s useful to know the symptoms of food poisoning that the various pathogens cause.

How do you know if you have an E. coli infection?

How do I know if I have a Salmonella infection?

How do you know if you have a Listeria monocytogenes infection?

If you think you do have food poisoning, you should see a doctor if your diarrhea is bloody, if you have a high fever over 101.5°, if you can’t keep fluids down, or if diarrhea lasts for more than three days. Other symptoms that should prompt a doctor’s visit include a decrease in urination, a very dry mouth, or feeling dizzy.