There is no widely accepted “gold standard” for detection of astroviruses in stool samples. Electron microscopy and cell culture isolation are expensive and cumbersome and may miss positive samples due to lack of sensitivity. On the other hand, highly sensitive assays based on EIA and PCR may be prone to false-positive results. In this report, we describe the development of an EIA based entirely on a group-specific MAb which reacts with human astrovirus serotypes 1 to 7. The advantages of a MAb-based assay include unlimited supplies of consistent reagents and avoidance of possible detection bias due to the use of polyclonal serum raised to a single serotype of astrovirus. Our EIA appears to be reasonably specific, with 78% of positives confirmed by tissue culture isolation.
In our survey, a possible etiologic agent was identified in 45% of stool samples from symptomatic pediatric inpatients, similar to the 47% reported in a prior study of nosocomial diarrhea in a Swedish pediatric hospital (4
). Previous studies of inpatient pediatric diarrhea from around the world have consistently shown that viral infections, particularly those due to RV, account for the majority of cases (4
). Among bacterial pathogens, C. difficile
is the most common cause of inpatient/nosocomial pediatric diarrhea (5
). Astrovirus, RV, and C. difficile
accounted for over 90% of the pathogens identified in our study, which included both community-acquired and nosocomial infections. We found that astroviruses accounted for approximately 10% of the diarrhea cases (21% of the identifiable cases) in this setting, which is comparable to previous reports (4
). We also observed an increased incidence of RV and astrovirus infections during winter months (data not shown), which is also consistent with previous reports (19
As seen in prior long-term surveys (20
), the majority (80%) of our clinical isolates were serotype 1 astroviruses. Serotype 1 strains were also predominant in two studies from children’s hospitals in England and Australia (26
). The variable reactivity of our serotype 1 isolates with MAb 5B7 and the isolation of three different serotypes demonstrate that multiple astrovirus strains were circulating in this children’s hospital during a single season.
Astrovirus infections occurred in a significantly younger patient population than either RV or C. difficile
infections in our studies. The decreased susceptibility of older patients to astrovirus infection suggests that astrovirus-infected infants may develop protective immunity to resist subsequent exposures. Very little is known about such immunity, although it is known that young children develop serum antibodies to astroviruses early in life (15
A novel observation in our study was the high rate of astrovirus infection in patients with short-bowel syndrome. Although this may have been due to ongoing environmental contamination or an unidentified carrier, other children on the same ward did not have as high an attack rate. These patients had undergone significant surgical intestinal resections and had lost not only absorptive surface area but large amounts of gut-associated lymphoid tissue, both of which losses may have rendered them particularly susceptible to symptomatic mucosal infection. Indeed, a 2 year old in our study with a very short gut excreted high titers of astrovirus for at least 45 days. Others have noted that patients with “underlying gastrointestinal disorders” were at increased risk for astrovirus-associated nosocomial diarrhea (9
All three of the major pathogens identified in this study may be found in stools of asymptomatic pediatric patients. Examination of 20 control stool samples from a ward with the highest number of symptomatic astrovirus-shedding patients showed that 6 were positive, suggesting that asymptomatic astrovirus infection can be quite common (data not shown). Prior studies of day care center outbreaks have also shown that asymptomatic astrovirus shedding is common among older attendees (24
). Further prospective case-control studies are warranted to fully assess the role of each of these pathogens in diarrheal disease of hospitalized pediatric patients.