Norovirus is a highly contagious virus that is a common cause of acute gastroenteritis, an inflammation of the stomach and intestines. This illness is often mistakenly called “stomach flu,” but it is not related to the influenza virus. Norovirus spreads easily through direct contact with an infected person, by touching contaminated surfaces, or by consuming contaminated food or water.
Clinical Assessment and Seeking Care
Healthcare providers often assess a suspected norovirus infection based on a patient’s symptoms and recent history. Common symptoms typically include sudden onset of nausea, vomiting, watery diarrhea, and stomach cramps, often accompanied by a low-grade fever, headache, or body aches. These symptoms usually appear 12 to 48 hours after exposure and generally resolve within one to three days. For most healthy individuals, a formal laboratory diagnosis is not pursued because the illness is self-limiting and resolves without specific medical treatment.
Seek medical attention if symptoms are severe or persistent, especially signs of dehydration like decreased urination, dry mouth, dizziness, or extreme fatigue. Young children, older adults, and individuals with weakened immune systems or other underlying medical conditions are at a higher risk for severe dehydration and complications, making medical consultation more important for these groups. Hydration support, including intravenous fluids, may be necessary if oral intake is insufficient.
Laboratory Testing Methods
When formal diagnosis is required, laboratory methods focus on detecting the norovirus in stool samples. Whole stool is the preferred specimen, collected within 48 to 72 hours of symptom onset when viral load is highest. Tests identify viral RNA (genetic material) or viral antigens.
Reverse Transcription Polymerase Chain Reaction (RT-PCR) is the most sensitive and specific method for detecting norovirus. This molecular test identifies as few as 10 to 100 norovirus copies by amplifying specific viral RNA regions. RT-PCR detects various norovirus genogroups and estimates viral load.
Enzyme-Linked Immunosorbent Assay (ELISA) detects norovirus antigens in stool samples. ELISA kits are rapid and inexpensive but have lower sensitivity and specificity than RT-PCR, potentially leading to false negative results. ELISA is often used for preliminary screening, especially during outbreaks, but negative results may require RT-PCR confirmation.
When is Formal Diagnosis Needed?
Formal norovirus diagnosis is not typically necessary for individual cases, as most healthy people recover quickly based on clinical symptoms. However, specific situations warrant laboratory testing for public health and clinical management.
Formal diagnosis is needed during suspected outbreaks in congregate settings like nursing homes, cruise ships, schools, or hospitals. Confirming norovirus helps public health authorities implement targeted infection control and surveillance to prevent further spread. Testing multiple specimens helps link cases and identify the outbreak source.
Formal diagnosis may also be pursued for vulnerable populations, including young children, the elderly, and immunocompromised individuals, where complications are more likely or illness prolonged. Testing is also important for differential diagnosis to rule out other pathogens causing similar gastrointestinal symptoms, such as bacteria or other viruses. This distinction ensures appropriate management and prevents unnecessary antibiotic use, which are ineffective against viruses.