THE CHANGING EPIDEMIOLOGY OF ASTROVIRUS-ASSOCIATED GASTROENTERITIS - A REVIEW

Our understanding of the epidemiology of astrovirus-associated gastroe nteritis has changed markedly with each improvement in detection metho d. In early surveys based on electronmicroscopy (EM), astroviruses app eared to be a rare cause of gastroenteritis, being found in fewer than 1% of children with diarrhea, usually in small outbreaks of disease a nd primarily during the winter season. The development and use of mono clonal antibodies and enzyme immunoassays (EIA) to detect astroviruses led to reports of a higher prevalence (2.5%-9%) of astrovirus infecti on among patients hospitalized with diarrhea. Astroviruses appeared se cond only to rotaviruses as a cause of hospitalization for childhood v iral gastroenteritis. Studies based on EIA detection of astroviruses i ndicate that astroviruses are common causes of diarrhea in children wo rldwide, and that most children are infected during their first two ye ars of life. The elderly and the immunocompromised represent high-risk groups as well. The observations that newborns monitored prospectivel y rarely have repeat disease and that the rate of detection decreases with increasing age suggest that immunity to astroviruses, as immunity to rotaviruses, may develop early in life. The cloning and sequencing of astroviruses have led to more sensitive assays to detect the virus es by reverse transcription, polymerase chain reaction (RT-PCR). Appli cation of RT-PCR for detection of astroviruses in children in day-care centers showed a marked increase in the detected prevalence of astrov irus-associated diarrhea, the rate of asymptomatic infection, and the duration of shedding of virus among those infected, when compared with studies that used other methods. As with rotaviruses, neither the mod e of transmission nor the reservoir of astrovirus infection has been i dentified. Both immune and molecular-based assays to detect astrovirus serotypes indicate that serotype 1 is most common worldwide, although the predominant serotypes may vary by region and time. In the absence of obvious strategies to prevent astrovirus-associated diarrhea, vacc ines might be considered if further studies establish that the disease burden would render such a vaccine cost-effective.