Description

Noroviruses (also referred to as “Norwalk-like viruses,” Norwalk viruses, human caliciviruses, and small round-structured viruses) are a common cause of acute gastroenteritis worldwide.

Norovirus infection presents as vomiting and diarrhea and often occurs in large outbreaks propagated by fecal-oral transmission via contaminated food or water or by direct person-to-person contact (1,2). Evidence also suggests that noroviruses can be transmitted via aerosolized vomit and contact with contaminated objects.

Occurrence

In the United States, norovirus infections are estimated to cause 23 million illnesses a year (3) and may cause up to 50% of all foodborne outbreaks. Seroprevalence studies in the Amazon, southern Africa, Mexico, Chile, and Canada have shown that norovirus infections are common throughout the world, and most children will have experienced at least one infection by the age of 5 years. Infection can occur year round.

Risk to Travelers

Travelers of all ages are potentially at risk for norovirus infection, and previous infection does not reliably result in subsequent immunity.

Risk of infection is present anywhere where food is prepared unhygienically or drinking water is inadequately treated. Of particular risk are “ready-to-eat” cold foods, such as sandwiches and salads (2). Raw shellfish, especially oysters, are also a frequent source of infection, since virus from contaminated water concentrates in the gut of these filter feeders (see Chapter 2).

Norovirus infection also has been associated with large outbreaks of gastroenteritis in various settings where persons living in close quarters, such as hotels, cruise ships, and camps, can easily infect each other over several days (4). Inapparent viral contamination of inanimate objects may persist during outbreaks and act as a source of infection. On cruise ships, for instance, such environmental contamination has caused recurrent outbreaks of illness on successive cruises with newly boarded passengers (1). Transmission of norovirus on an airplane may be limited if vomiting is confined to restrooms and sick persons are kept separate from others (5).

Clinical Presentation

Infected persons usually have acute-onset, violent vomiting and nonbloody diarrhea after an incubation period of 24-48 hours. Other symptoms include abdominal cramps, nausea, and occasionally a low-grade fever. Illness is generally self-limited, and full recovery can be expected in 1-4 days. In some cases, dehydration, especially in those who are very young or elderly, may require medical attention. (For infants, please refer to Table 8-1 for Assessment of Dehydration Levels for Infants.)

Prevention

No vaccines are available. Noroviruses are very common and highly contagious, but the risk of infection can be mini-mized by frequent and proper handwashing and avoidance of possibly contaminated food and water.

In addition to handwashing, measures to prevent transmission of noroviruses between persons traveling together include careful clean-up of fecal material or vomit and disinfection of contaminated surfaces and toilet areas with products approved for norovirus disinfection by the Environmental Protection Agency or a high concentration of domestic bleach (at least a 1:5 solution of bleach and water) (6). Soiled articles of clothing should be washed promptly and thoroughly and machine-dried at high heat. Confinement of ill persons to help prevent the spread of noroviruses has occasionally been implemented on cruise ships.

Treatment

No antiviral medication is available for treating norovirus infection. Supportive care, such as rest and oral rehydration, is the mainstay of management. (See Table 4-20, Composition of World Health Organization Oral Rehydration Solution [ORS] for Diarrheal Illness.)

References

1. Widdowson MA, Cramer EH, Hadley L, Bresee JS, Beard RS, Bulens SN, et al. 2004 Outbreaks of acute gastroenteritis on cruise ships and on land: identification of a predominant circulating strain of norovirus—United States, 2002; J Infect Dis. 2004;190:27-36.
2. Bresee JS, Widdowson M-A, Monroe SS, Glass RI. Foodborne viral gastroenteritis: challenges and opportunities. Clin Infect Dis. 2002;35:748-53.
3. Mead PS, Slutsker L, Dietz V, McCaig LF, Bresee JS, Shapiro C, et al. Food-related illness and death in the United States. Emerg Infect Dis. 1999;5:607-25.
4. CDC. Norovirus activity, United States, 2002. MMWR Morbid Mortal Wkly Rep. 2003;52:41-5.
5. Widdowson M-A, Glass RI, Monroe S, Beard RS, Bateman JW, Lurie P, et al. Probable transmission of norovirus on an airplane. JAMA. 2005;293:1859-60.
6. CDC. Norwalk-like viruses: public health consequences and outbreak management. MMWR Morbid Mortal Wkly Rep. 2001;50:(RR-9).