Asymptomatic cases may fuel nosocomial astrovirus

Synopsis: Astrovirus was identified in stool of 12.7% of hospitalized infants and children with diarrhea; half of the cases were nosocomially acquired.

Source: Shastri S, et al. Prevalence of astroviruses in a children’s hospital. J Clin Microbiol 1998; 36:2,571-2,574.

Shastri and colleagues at Stanford University screened 357 stool samples from 267 pediatric inpatients with diarrhea for presence of astrovirus by enzyme immunoassay. The clinical laboratory did routine examinations for other pathogens.

Clostridium difficile toxin was identified in stool of 12.7% of the patients, rotavirus in 11.6%, and astrovirus in 9.7%. Together they accounted for 90% of the pathogens identified. Other pathogens identified in smaller numbers of patients were bacteria, protozoans, and adenovirus.

A second pathogen was identified in stool of six (23%) of the 26 patients with astrovirus infection. One-half of the astrovirus infections were considered nosocomial in origin. Four patients were studied serially; astrovirus shedding lasted less than 14 days in two, at least 10 days in one, and for at least 45 days in a child who previously had a resection of a large portion of his small intestine. Seventy-eight percent of the EIA-positive samples were confirmed by isolation in tissue culture. Fifteen (83%) of the 18 tissue culture-adapted isolates of astrovirus were of serotype 1, two were serotype 2, and one was serotype 3.

Six (30%) of 20 stool samples obtained from children without diarrhea who were residing in a ward with the greatest number of symptomatic cases of astrovirus infection also were positive for astrovirus. Most of the children in this tertiary care facility had serious underlying disease. One of these abnormalities, short bowel syndrome, was present in six (23%) of the 26 patients with astrovirus infection.

Comment: Stan Deresinski, MD, FACP, associate chief of infectious diseases, Santa Clara Valley (CA) Medical Center.

Viruses account for the majority of cases of pediatric diarrhea worldwide, and C. difficile is the leading cause of nosocomially acquired diarrhea in children. This and other studies have found that astroviruses are second only to rotaviruses as a cause of pediatric diarrhea. In addition to the role of these single-stranded RNA viruses in causing both community- and hospital-acquired diarrhea in infants and children, astroviruses can affect adults. They have, in fact, been identified as an etiologic pathogen in an outbreak of diarrhea occurring in a residential home for the elderly.¹

Previous studies have found an incidence of astrovirus in association with diarrhea in infants similar to that reported by Shastri et al. Its association with pediatric nosocomial infection has been confirmed in many of these studies. The frequent detection of the virus in the stool of asymptomatic children who shared a ward with symptomatic patients with this infection suggests that nosocomial transmission is even more common than found here and that excretion of virus by asymptomatic individuals is an important reservoir of infection. The incidence of astrovirus infections peaks in the winter months in temperate climates. Now that a vaccine against rotavirus infection is available, astrovirus diarrhea will assume increasing importance. For most of us, however, the ability to diagnose this infection awaits development of commercially available assays.

Reference

1. Gray JJ, et al. An outbreak of gastroenteritis in a home for the elderly associated with astrovirus type 1 and human calicivirus. J Med Virol 1987; 23:377-381.