Outbreaks of viral gastroenteritis have occurred in nursing homes and institutional residences. Risk factors in such settings include the enclosed living quarters in which most residents spend their time and the decreased personal hygiene among some residents because of incontinence, immobility, or reduced alertness.
The most common cause of outbreaks in nursing homes are by the Norwalk virus, which has an average incubation period was 24-48 hours and the average duration of illness was 12-60 hours.
Most outbreaks of viral gastroenteritis are self-limited; however, certain factors create risks of intense or prolonged transmission that may require aggressive intervention. These risk factors include a closed environment (e.g., nursing home), a constantly renewing population of susceptible persons (e.g., children at camp), or persons at special risk (e.g., the elderly). Whatever the initial source of the outbreak, subsequent viral transmission is often person-to-person, with both direct fecal-oral and airborne transport probably involved. Although interruption of this transmission may be difficult, the following measures may be helpful in controlling the spread of infection.
Identify and Eliminate a Common Source
For Norwalk virus outbreaks, an ill food handler is a likely source, although water, ice, and shellfish are other common sources. When a water supply is thought to be contaminated with Norwalk virus, shock chlorine concentrations (greater than or equal to 10 mg/L for 30 minutes or longer) may be helpful. Prevent Employee Transmission of Illness
In many settings, employees (e.g., health-care providers, staff of day-care centers) are at highest risk for transmitting disease because of their many contacts with ill persons. Any staff member with symptoms that suggest infection should be excluded from contact with potentially susceptible persons for at least 2 days after resolution of illness. This exclusion is particularly important for food handlers, who also should not be involved in preparing food for the same period. Prevent Employee Acquisition of Illness
Personnel coming into direct contact with ill persons should wear disposable plastic gloves. When contamination of clothing with fecal material is possible, personnel should also wear gowns. Hands, which are the most likely means by which viral spread occurs, should be washed after each contact. The recommended procedure is to rub all surfaces of lathered hands together vigorously for at least 10 seconds, with plain soap or an antimicrobial-containing product, and then thoroughly rinse the hands under a stream of water. Since spattering or aerosols of infectious material may be involved in disease transmission, wearing of masks should be considered, particularly by persons who clean areas grossly contaminated by feces or vomitus. Use Safeguards with Laundry
Soiled linens and clothes should be handled as little as possible and with minimum agitation to prevent microbial contamination of the air and of persons handling the linen. Laundry should be transported in an enclosed and sanitary manner (e.g., in a plastic bag if the laundry is wet or moist), promptly machine washed with a detergent in water at the maximum cycle length, and then machine dried.
Clean Soiled Surfaces
Because environmental surfaces in certain settings have been implicated in the transmission of enteric viruses, bathrooms and rooms occupied by ill persons should be kept visibly clean on a routine basis. Surfaces that have been soiled, especially by feces or vomitus, should first be cleaned of visible material and then disinfected with an appropriate commercial germicidal product according to the manufacturer's instructions. Feces and vomitus collected during the cleaning procedure should be promptly disposed of in a manner that prevents transfer of this material to other surfaces or persons. Persons performing these tasks should wear appropriate protective barriers (e.g., utility gloves--and if splashing is anticipated, a mask or face shield and garments such as a uniform, jumpsuit, or gown to protect street clothing).
Minimize Contact Between Well and Ill Persons
When possible, ill persons should be separated from well persons until at least 2 days after resolution of symptoms. If nosocomial rotavirus is involved, this period should be longer--at least until the ill person's stool is negative by antigen detection, which may be greater than or equal to 1 week.

Norwalk-like Viruses
Levels of antibody specific to the Norwalk agent are low during childhood but reach 50% by middle age.
Clinical syndrome
The incubation period is 24-48 hours, and the mean duration of illness is 12-60 hours. Nausea is prominent, with vomiting, non-bloody diarrhea, and abdominal cramps occurring in most cases. These symptoms are experienced by all age groups, but diarrhea is relatively more prevalent among adults. From 25%-50% of affected persons also report headache, fever, chills, and myalgias. Adults have died during illness caused by Norwalk-like viruses, presumably from electrolyte imbalance. Late sequelae have not been reported, but the elderly often report persistence of constitutional symptoms for up to several weeks.

Mode of transmission
Routes of transmission that have been documented include water, food(particularly shellfish and salads), aerosol, fomites, and person-to-person contact. Infectivity can last for as long as 2 days after resolution of symptoms. Presymptomatic shedding has been suspected. Aerosolized or splattered Norwalk-like particles have been implicated in the transmission of gastroenteritis. Aerosolized rotavirus has caused diarrheal illness in mice, and airborne transmission of this agent among humans has been suspected. Studies are needed to address the efficacy of barrier precautions (e.g., face shields, respirators) in interrupting transmission of these agents.
Outbreak characteristics Numerous reports have described the course of outbreaks caused by Norwalk-like agents, usually involving adults and older children. Outbreaks are generally limited to 1-2 weeks unless transmission is facilitated by a closed environment (e.g., a nursing home).

For more assistance with a GI outbreak, contact your local county health department.