Norovirus Infection (cont.)

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What is the incubation period for a norovirus infection? How long are people infected with norovirus contagious?

Norovirus may have a prolonged infection period that starts even before someone gets sick. There is a short lag or incubation period (up to two days) between the time that people acquire the virus and the time they get symptoms. People may be contagious during this period. All people are contagious while they are having symptoms or showing signs.

Although the most contagious period is over when the patient's symptoms resolve, even some people who appear to have recovered completely after a norovirus infection may continue to shed the virus for weeks in their stool and may be a source of infection to others. People with compromised immune systems (for example, those receiving chemotherapy or undergoing organ transplant) may shed the virus for months. However, in general, most individuals become noncontagious about 72 hours after symptoms have resolved. Consequently, although it may be difficult for parents to do so, children and adults should not go back to school, day care, or work until they have been symptom-free for three days.

How is a norovirus infection diagnosed?

Because the symptoms of norovirus are similar to those of other common viral diarrheas like rotavirus, it is necessary to do specific tests to identify the virus. Norovirus cannot be cultured in a laboratory. However, the RNA inside the virus may be detected directly using polymerase chain reaction (PCR) tests, and these tests are the ones that are most commonly used. Enzyme-based immunoassays (EIA) can also be used to detect the virus in stool samples. EIAs use special antibodies that attach to virus particles. In addition, the Ridascreen Norovirus 3rd Generation EIA assay is approved for use to detect norovirus when a number of people have simultaneously contracted gastroenteritis and there is a clear avenue for virus transmission, such as a shared location or food source. However, this new test is not sensitive enough for definitive diagnosis of norovirus infection in an individual. The human body makes antibodies against norovirus, and these can be identified with immunoassay testing of blood samples. Unfortunately, it takes 10-14 days for the body to make antibodies, so this test is not useful for real-time diagnosis. It is also possible to see the virus particles using electron microscopy, although this is mostly a research tool. Currently, the preferred test for norovirus according to the CDC is the PCR test. This test helps distinguish between other diseases (for example, rotavirus and Salmonella infections) that may produce similar symptoms.

Once norovirus has been confirmed in an outbreak setting, it is not necessary to test every person. Rather, people with typical symptoms are assumed to have acquired the virus.

Medically Reviewed by a Doctor on 10/28/2015

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Norovirus Infection - Symptoms Question: What were the symptoms associated with a norovirus infection in you or someone you know?
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