Public Health England advises that while it may be tempting to deduce that a gastrointestinal illness occurring soon after a ‘suspect’ meal is food poisoning, the true culprit may not be obvious as pathogen incubation periods can range significantly from a couple of hours to over a week. Symptoms and how they change over time may therefore suggest which pathogen might be involved.3

Bacillus spp will cause nausea and vomiting (emetic syndrome) initially within 1-6 hours of ingestion, and then progress to diarrhoea from 6 to 24 hours after ingestion. Staphylococcus aureus can have a similarly swift onset of 2-4 hours, with vomiting and abdominal pain.3

Salmonella spp may take between six hours and three days but usually 12-36 hours, with diarrhoea, vomiting and fever. C. perfringens typically causes diarrhoea and abdominal pain between 4-24 hours after ingestion, but usually 8-12 hours.

Campylobacter spp takes 1-10 days (but usually 2-5 days) to show and is associated with abdominal pain and profuse diarrhoea which may even be blood stained, but vomiting is uncommon. Depending on the strain, E coli onset of symptoms can range from 9 hours to 8 days. E coli tends to have diarrhoea (sometimes with blood) as the main symptom.

Shigella spp incubation is between 12 hours and 7 days, but typically 1-3 days. Shigella sonnei is usually associated with mild diarrhoea, but other species may cause more severe diarrhoea and even dysentery type symptoms.

Norovirus symptoms may come on suddenly but the virus will have been incubating 10 to 50 hours, typically 1-2 days. Rotavirus has an incubation period of 2 days.3,23,24

Duration of contagiousness also varies: while norovirus symptoms last 1-2 days, the patient is likely to be contagious for a few more days and the virus may still be being shed or excreted after more than two weeks. Someone with rotavirus can be contagious before symptoms appear.25