1. Basic Facts About Norovirus
What Is Norovirus?
Norovirus is a highly contagious virus that is responsible for gastroenteritis (inflammation of the intestines) in humans that is usually referred to as a norovirus infection. The specific virus responsible for causing illness in humans is the Norwalk virus, which is part of the Norovirus group. Norovirus is also referred to as the stomach flu or winter vomiting bug. It is responsible for a considerable number of inpatient and outpatient visits every year.
Norovirus infection results in inflammation of the intestinal tract, which can result in sudden onset of severe diarrhea and vomiting. Some people also experience pain or cramps in the abdominal region, low-grade fever, muscle aches and pains, general feelings of discomfort, and nausea. In some cases extreme dehydration may result. In most people, symptoms last between one and three days, but traces of norovirus can remain in fecal deposits for up to several weeks or even months. Some carriers of the virus are asymptomatic (showing no common signs or symptoms of the pathogen) but are still contagious.1
How Contagious Is Norovirus?
As few as 18 particles of the virus are needed to spread the pathogen to another person, making it extremely contagious.2 This explains its ability to spread quickly, especially in closed environments such as schools, colleges, day-care centers, cruise ships and prisons. Individuals are most contagious when they are symptomatic and during the three days after recovery.
Norovirus Incubation Period
The incubation period refers to the time between first exposure to a virus or infection and the appearance of symptoms commonly associated with the virus. According to the Centers for Disease Control and Prevention (CDC), the incubation period after exposure to norovirus is 12 to 48 hours, with the average period being around 33 hours.2
Who Is at Risk?
Everyone is at risk of norovirus, but the elderly, infants and people already experiencing acute or chronic comorbidities are at increased risk. Elderly patients in long-term care facilities are particularly at risk if a norovirus outbreak occurs due to general decreased strength and ability to fight off disease and illness. Patients with compromised immune systems, such as those undergoing chemotherapy or organ transplant, or those with a coinfection resulting from HIV, are also at increased risk. Immunosuppressed patients are unable to recover as quickly from norovirus, in some cases developing chronic symptoms that persist for weeks to years.3
How Is Norovirus Diagnosed?
A clinical diagnosis based on signs and symptoms usually determines whether a patient has norovirus. In outbreak situations, when the source of the outbreak needs to be determined, norovirus can be detected by measuring levels of viral RNA in fecal specimens from infected patients using a reverse transcription-polymerase chain reaction (RT-PCR) assay. This assay is available at most state public health laboratories.2