Viral agents of gastroenteritis: public health importance and outbreak management

Morbidity and Mortality Weekly Report, April 27, 1991

In the United States, the peak incidence of rotavirus diarrhea is among children 6 months-2 years of age, although in developing countries younger infants may be affected. By 4 years of age, most persons have been infected and are immune to the severe dehydrating syndrome, but a high inoculum or lowered immunity can produce milder illness among older children or adults. One-third of parents whose children are infected with rotavirus become ill (7), and rotavirus diarrhea can occur among travelers to developing nations, the elderly, and persons with debilitative or immunosuppressive conditions. In the United States, rotavirus activity is concentrated in the cooler months of the year (October-April).

Clinical syndrome

In general, the incubation period is approximately 2 days and is followed by vomiting for 3 days and watery diarrhea for 3-8 days. Fever and abdominal pain occur frequently. Usually, there are no sequelae other than temporary intolerance of lactose; however, without adequate fluid replacement the syndrome can result in severe dehydration and death.

Modes of transmission

A person with rotavirus diarrhea may excrete approximately 1 trillion infectious particles/milliliter of stool. Since the infective dose in a child can be as few as 10 particles (8), person-to-person transmission probably perpetuates endemic disease. Infectivity does not parallel the presence of symptoms. Asymptomatic rotavirus excretion has been reported among half of children the day before diarrhea starts and among one-third during the week after symptoms end (9). Many children can shed rotavirus and never become ill (10, 11). When food or water is contaminated to the extent that it overcomes adult immunity, rotavirus diarrhea among adults may be relatively common. in Thailand, 5% of adult gastroenteritis has been found to be caused by rotavirus (12). Outbreak characteristics

Nosocomial rotavirus among pediatric populations is common; in one study, all children hospitalized for >2 weeks during rotavirus season ultimately shed the virus (13). Rotavirus at day-care centers, in both endemic and outbreak form, is also common (9,14,15). Outbreaks in neonatal units are frequently reported, but infection among full-term infants is usually benign, perhaps because maternal antibody transferred during the third trimester protects against illness for the first 3-6 months of life; premature infants are at higher risk. Among adults, an outbreak arising from rotavirus contamination of a municipal water supply has been reported (16), and foodborne transmission was suspected in two other outbreaks involving banquets (CDC, unpublished data). immunity

infection generally confers long-term immunity to serious gastroenteritis (17), but asymptomatic or minimally symptomatic reinfection can occur throughout life. Immunity may wane among the elderly, rendering them susceptible again to severe disease.

Atypical rotaviruses

Rotaviruses affecting humans were once thought to be limited to one antigenic family termed Group A, whereas other antigenic groups (B-E) were thought to be strictly zoonotic. In 1982, however, an epidemic of Group B rotavirus affected millions of persons in China (including adults, children, and neonates) (18), and since then outbreaks have recurred, although affecting fewer persons. Studies of immunoglobulin pools from Shanghai suggest that the Chinese population had been exposed to this pathogen in the past (19). Since Group B rotavirus is a common diarrheal pathogen for swine, and since all rotaviruses have a segmented genome (similar to influenza) capable of antigenic changes through reassortment of genes, investigators have hypothesized that this human Group B epidemic arose by a reassortment that allowed the swine virus to propagate in the human gut (20). Thus far, the Group B epidemic is not known to have spread beyond China, despite serologic evidence of human infection in Southeast Asia. Group C rotaviruses are also primarily swine pathogens but have been detected among humans in all parts of the world. Outbreaks have occurred in Japan and England, but the importance of Group C rotaviruses in endemic disease is unknown (21,22). Although both Group B and Group C rotaviruses in humans have been reported in the United States, serum studies suggest that exposure has been minimal in the past. With the U.S. population almost wholly susceptible, the extent to which these atypical rotaviruses represent a potential public health hazard in the United States is unclear.