Norovirus Infection
Abstract & Commentary
Synopsis: Noroviruses are the most common cause of gastroenteritis in the United States, accounting for approximately 23 million cases annually.
Source: CDC. MMWR Morb Mortal Wkly Rep. 2003;52:41-45.
Noroviruses are a frequent cause of acute gastroenteritis. During the last 2 months of 2002 in a single health district in Washington state, 10 outbreaks of acute gastroenteritis attributable to norovirus were investigated. These events affected 354 patients in 6 long-term care facilities, a community hospital, an outpatient clinic, and the county jail.
In New Hampshire in 2002, 29 outbreaks of norovirus gastroenteritis in long-term care facilities (28 in a single month) and 2 outbreaks each in restaurants, schools, and residential summer camps were investigated. These investigations implicated person-to-person, food-borne, and water-borne transmission in 32, 2, and 1 outbreak, respectively.
Investigation of 66 outbreaks affecting approximately 1700 people in New York City occurring during 2 winter months of 2002-2003 implicated norovirus infection. Fifty-one percent occurred in nursing homes, long-term care facilities, and rehabilitation facilities; 10 in hospitals; 3 in restaurants; and 1 each in a school and a homeless shelter.
Of 27 norovirus outbreaks investigated by the CDC, 11 (41%) were caused by a single strain, the Farmington Hill strain. Although not epidemiologically related, 6 of the Farmington Hill strain outbreaks occurred on land and 5 on cruise ships.
Comment by Stan Deresinski, MD, FACP
In 1972, viral particles were detected by immune electron microscopy in the stools of volunteers at the NIH who had ingested filtrates of stool obtained during an outbreak of diarrheal illness.1 The virus was named after the site of that 1968 outbreak in Norwalk, Ohio.2 Many subsequent outbreaks of what was called winter vomiting disease were found to be caused by Norwalk-like viruses, now called noroviruses. This small, positive-sense, single-stranded RNA virus belongs to the family Calciviridae. Noroviruses have resisted cultivation, and there are no animal models. The development of an RT-PCR assay on stool has facilitated our understanding of the epidemiology of norovirus infection.
While outbreaks of norovirus infection on cruise ships have been in the news lately,3 the majority of outbreaks occur in settings on land such as nursing homes, restaurants, schools, and day care centers. Noroviruses may also account for more than 10% of sporadic cases of gastroenteritis in both children and adults. In 1996-1997, 86 of 90 outbreaks (96%) of nonbacterial gastroenteritis in the United States were due to Norwalk-like viruses.4 The incidence of norovirus infections appears to be increasing for reasons that are not understood.
The illness caused by Norovirus often presents, after an incubation period of 24-48 hours, with vomiting, diarrhea, nausea, and abdominal pain. Fever occurs in no more than one-half of cases and is low grade and transient. The illness generally lasts 1-3 days. The features that identify an outbreak of gastroenteritis as possibly due to Norovirus are listed in the Table below.5
| Table |
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Features of Gastroenteritis Outbreaks Consistent with Norovirus |
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Etiology
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Cases result from ingestion of contaminated food or water or from direct person-to-person transmission. Implicated food is characteristically served cold such as salads and sandwiches. Norovirus is probably also transmitted by droplet formation from vomitus. Persistent environmental contamination may be important in the epidemiology of the disease. Environmental contamination and person-to-person transmission account for secondary cases occurring in outbreaks, a feature characteristic of norovirus disease.
The infectious dose is as few as 10 viral particles. Asymptomatic shedding may persist for up to 2 weeks, and the virus is stable in the environment, being capable of surviving freezing, heating to 60°C, and as much as 10 ppm of chlorine. These factors, together with its multiple modes of transmission, wide strain diversity, and the transient nature of immunity to infection, account for the frequent outbreaks due to norovirus.6
Vaccine development may be problematic, given the existence of multiple strains of norovirus, as well as the transient nature of immunity after infection. In the meantime, the only means of control is prevention by maintenance of good food, environmental, and personal hygiene.
Dr. Deresinski is Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, Santa Clara, Calif.
References
1. Kapikian AZ, et al. J Virol. 1972;10:1075-1081.
2. Adler JL, Zickl R. J Infect Dis. 1969;119:668-673.
3. MMWR Morb Mortal Wkly Rep. 2002;51:1112-1125.
4. Fankhauser RL, et al. J Infect Dis. 1998;178: 1571-1578.
5. Kaplan JE, et al. Ann Intern Med. 1982;96:756-761.
6. Bresee JS, et al. Clin Infect Dis. 2002;35:748-753.
Noroviruses are the most common cause of gastroenteritis in the United States, accounting for approximately 23 million cases annually.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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