The term “stomach flu” is a common name for acute gastroenteritis, an infection of the intestines, not the influenza virus. This highly contagious illness is typically caused by viruses, most notably Norovirus and Rotavirus. Understanding the duration of contagiousness is important because transmission can occur before symptoms begin and for a long time after they resolve. These viruses are easily spread through contact with the stool or vomit of an infected person, often via contaminated surfaces or food. Determining the risk to others depends heavily on the specific pathogen involved.
Contagious Timelines by Pathogen
Norovirus is the most common cause of viral gastroenteritis and is extremely contagious, requiring only a small number of viral particles to cause infection. Contagiousness often begins before symptoms appear, with the period of highest risk occurring when vomiting and diarrhea are at their worst. While symptoms usually last only one to three days, the intense acute phase means the person is actively shedding billions of virus particles. A person should be considered highly infectious from the moment they start feeling ill until at least 48 hours after all symptoms have completely stopped.
Rotavirus primarily affects infants and young children and also has a contagious period that starts before the onset of symptoms. Rotavirus symptoms tend to last longer than norovirus, often spanning three to eight days. Similar to norovirus, virus shedding is highest during the acute symptomatic phase when severe watery diarrhea is present.
Risk of Transmission After Recovery
Viral Shedding
The risk of transmission does not end once the acute symptoms have resolved, due to a phenomenon called viral shedding. Viral shedding refers to the continued release of infectious virus particles in the stool, even when the person feels completely better. For norovirus, a person can continue to shed the virus in their stool for three days up to two weeks or more following recovery.
Post-Symptomatic Risk
This prolonged shedding presents a hidden danger for community spread, especially in environments like schools, daycares, or workplaces. Rotavirus shedding can also extend well past the end of symptoms, sometimes lasting up to 10 days or even longer after recovery. Because of this, public health recommendations often advise children and food handlers to stay home for at least 48 hours after their last episode of vomiting or diarrhea to minimize the chance of post-symptomatic spread.
Preventing Spread in the Home and Community
Rigorous hand hygiene is the most effective measure to prevent transmission, particularly because these viruses spread easily through the fecal-oral route. Unlike many other germs, Norovirus is relatively resistant to alcohol-based hand sanitizers, making frequent and thorough handwashing with soap and water the preferred method. Hands should be washed after using the restroom, before preparing food, and after changing diapers or assisting someone who is ill.
Environmental disinfection is also a necessary step to mitigate the spread of these resilient viruses, which can survive on surfaces for days or weeks. Standard household cleaners are often insufficient for Norovirus, so a bleach-based household disinfectant must be used on contaminated surfaces. High-touch surfaces should be cleaned diligently, especially following an episode of vomiting or diarrhea. Examples of high-touch surfaces include:
- Doorknobs
- Light switches
- Faucets
- Countertops
Contaminated clothing and bedding should be washed separately on the hottest cycle possible to destroy any lingering viral particles.