Norovirus infection overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Noroviruses are a group of viruses that cause gastroenteritis, which is commonly known as the "stomach flu" or "food poisoning", in people. The term norovirus was recently approved as the official name for this group of viruses. Norovirus is a very contagious virus. One can get norovirus from an infected person, contaminated food or water, or by touching contaminated surfaces. The virus causes stomach or intestines or both to get inflamed (acute gastroenteritis). This leads to stomach pain, nausea, diarrhea and vomiting. Anyone can be infected with norovirus and get sick. Also, norovirus infection can occur many times in life. Norovirus illness can be serious, especially for young children and older adults. Norovirus is the most common cause of acute gastroenteritis in the United States. Each year, it causes about 21 million illnesses and contributes to about 70,000 hospitalizations and 800 deaths. Norovirus is also the most common cause of foodborne-disease outbreaks in the United States. The best way to help prevent norovirus is to practice proper hand washing and general cleanliness.
Pathophysiology
Norovirus is a highly contagious virus. Anyone can get infected with norovirus and get sick. Also, one can get norovirus illness many times in life. One reason for this is that there are many different types of noroviruses. Being infected with one type of norovirus may not protect one against other types. Norovirus can be found in your stool (feces) even before one starts feeling sick. The virus can stay in stool for 2 weeks or more after one feels better.
Causes
Norovirus causes norovirus infection in people. Noroviruses (genus Norovirus, family Caliciviridae) are a group of related, single-stranded RNA, nonenveloped viruses that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as “Norwalk-like viruses” (NLV). Noroviruses belong to the family Caliciviridae that includes sapoviruses, which also causes acute gastroenteritis.
Risk Factors
Noroviruses are transmitted directly via person to person or indirectly via contaminated water and foods. A CDC study of eleven outbreaks in New York State lists the suspected mode of transmission as person-to-person in seven outbreaks, foodborne in two, waterborne in one, and one unknown. The source of waterborne outbreaks may include water from municipal supplies, wells, recreational lakes, swimming pools and ice machines. [1]
Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks. Ingestion of raw or insufficiently steamed clams and oysters poses a high risk for infection with the Norwalk virus. Foods other than shellfish are contaminated by ill food handlers.[2]
Natural History, Complications and Prognosis
The incubation period for norovirus-associated gastroenteritis in humans is usually between 24 and 48 hours (median in outbreaks 33 to 36 hours), but cases can occur within 12 hours of exposure. Recovery is usually complete and there is no evidence of any serious long-term sequelae.
Diagnosis
History and Symptoms
Norovirus infection usually presents as acute-onset vomiting, watery non-bloody diarrhea with abdominal cramps, and nausea. Low-grade fever also occasionally occurs, and vomiting is more common in children. Dehydration is the most common complication, especially among the young and elderly, and may require medical attention. Symptoms usually last 24 to 60 hours.
Physical Examination
Norovirus infection can present as mild febrile illnesss or a severe febrile illness with temperatures of 101-102 F.
Laboratory Findings
In the last 10 years, diagnosis of norovirus as cause of outbreaks of acute gastroenteritis has improved with the increasing use of the reverse transcriptase polymerase chain reaction (RT-PCR). Currently, state public health laboratories of 47 states have the capability to test for noroviruses by (realtime) RT-PCR. RT-PCR detects the norovirus RNA and can be used to test stool and emesis samples, as well as environmental swabs in special studies. Identification of the virus can be best made from stool specimens taken within 48 to 72 hours after onset of symptoms, although good results can be obtained by using RT-PCR on samples taken as long as 5 days after symptom onset. Virus can sometimes be found in stool samples taken as late as 2 weeks after recovery.
Sequencing of norovirus strains found in clinical and environmental samples has greatly helped in conducting epidemiologic investigations by linking cases to each other and to a common source and by differentiating outbreaks that were mistakenly connected. Sequences can be entered into CaliciNet, a recently developed sequence database on the basis of the PulseNet model. In the next years CaliciNet will be further implemented to be able to help to determine links (e.g., norovirus contaminated foods) between outbreaks across the U.S.
Older methods for diagnosis include direct and immune electron microscopy of fecal specimens, and detection of a fourfold increase of specific antibodies in acute- and convalescent-phase blood samples. Several commercially available enzyme-linked immunosorbent assays for detection of virus in stools have been developed but await evaluation further evaluation regarding sensitivity and specificity.
Treatment
Medical Therapy
There is no specific medicine to treat people with norovirus illness. Norovirus infection cannot be treated with antibiotics because it is a viral (not a bacterial) infection. Patients with norovirus infection should drink plenty of liquids to replace fluid lost from throwing up and diarrhea. This will help prevent dehydration. Sports drinks and other drinks without caffeine or alcohol can help with mild dehydration. But, these drinks may not replace important nutrients and minerals. Oral rehydration fluids that you can get over the counter are most helpful for mild dehydration. Dehydration can lead to serious problems. Severe dehydration may require hospitalization for treatment with intravenous fluids).
Primary Prevention
There is no vaccine to prevent norovirus infection. Prevention of foodborne norovirus disease is based on the provision of safe food and water. Noroviruses are relatively resistant to environmental challenge: they are able to survive freezing, temperatures as high as 60°C, and have even been associated with illness after being steamed in shellfish. Moreover, noroviruses can survive in up to 10 ppm chlorine, well in excess of levels routinely present in public water systems. Despite these features, it is likely that relatively simple measures, such as correct handling of cold foods, strict hand washing after using the bathroom and before handling food items, and paid sick leave, may substantially reduce foodborne transmission of noroviruses. Prevention of norovirus disease spread via droplets from vomitus (person to person transmission) should focus on methods to limit transmission including isolation precautions (e.g., cohort sick patients in a healthcare facility) and environmental disinfection.
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Information to Young Families
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Information to Hospital Visitors
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References
- ↑ Hedberg CW, Osterholm MT (1993). "Outbreaks of food-borne and waterborne viral gastroenteritis". Clin. Microbiol. Rev. 6 (3): 199–210. PMID 8395330.
- ↑ Parashar UD, Monroe SS (2001). ""Norwalk-like viruses" as a cause of foodborne disease outbreaks". Rev. Med. Virol. 11 (4): 243–52. doi:10.1002/rmv.321. PMID 11479930.