The common bacteria Staphylococcus aureus causes skin infections (see “Staph”). If a food handler has a tiny (or big) infection, & the germ gets to their hands, it can wind up in food. Mayonnaise, salad dressing, eggs, dairy products, & cold cuts are favorite foods for the germ to grow on. Sometimes large numbers of banquet guests ingest it.
Staph gives off a toxin. Symptoms begin 1 to 8 hours after the meal. There’s mostly nausea & vomiting, that begin abruptly. They can go on for hours. Sometimes there’s diarrhea too, but that’s usually minor compared to the vomiting. We make the diagnosis based on symptoms alone — lots of sudden vomiting, with no other signs to suggest anything more serious. This is only “poisoning” in the technical sense; the bacteria makes a “toxin,” & toxin means “poison,” although the person isn’t really “poisoned” in the common use of the word.
There’s no treatment, except staying hydrated by sipping small amounts of fluids, frequently (like every 20 minutes). Once you’ve vomited all the toxin out, usually within 12 hours or less, everything gets better. Medicines to relieve vomiting help you stay sick longer (with a toxin in the belly, vomiting is indeed its own treatment!).
The viruses Norovirus & Rotavirus are famous for causing gastroenteritis. They primarily cause diarrhea, and lots of it, but may begin with just vomiting for 1 to 2 days. See Acute Gastroenteritis for a discussion of the many germs that cause diarrhea.