After contaminated food is eaten, there is a delay before the consumer starts to feel the first food poisoning symptoms. This delay is called the “incubation period”. Incubation periods of foodborne illnesses can range from a few hours to several days or weeks. 
People tend to believe that the last food they ate caused their illness. This is not always the case (and is almost always incorrect). As seen below, it usually takes at least 12 hours for common foodborne pathogens to have a symptomatic affect on the consumer.
Health investigators routinely use known incubation periods to work backwards to determine the likely source of a person’s illness. The reported incubation periods vary to some degree, but below is a compilation of recent values from the CDC, FDA, and state and local health departments:
| Pathogen | Typical Incubation | Incubation Range |
| Clostridium Botulinum (Botulism) | 12 – 36 hours | 6 hours - 10 days |
| Salmonella | 18 – 36 hours | 6 – 72 hours |
| Shigella | 24 – 72 hours | 12 hours – 7 days |
| Campylobacter | 3 – 5 days | 1 – 10 days |
| E Coli 0157:H7 | 2 – 5 days | 1 – 10 days |
| Listeria | 20 – 30 days | 1 – 90 days |
| Hepatitis A | 25 – 30 days | 10 – 50 days |
