“24-hour illnesses” are normally caused by noroviruses, which are a type of virus that is responsible for the “stomach flu” and its symptoms. Although they are nicknamed 24 hour illnesses, the illnesses caused by noroviruses can last up to 10 days and require a visit to a local family physician or even the ER in rare cases. Most of the time noroviruses are not serious and may not even require a trip to a family physician.