Nosocomial outbreak of infant rotavirus diarrhea due to the appearance of a new serotype 4 strain

An outbreak of acute gastroenteritis, involving 30 infants and young children aged 2 months to 4 years, took place in a pediatric ward of the University Hospital of Pavia, Northern Italy, in the period from November 9 to December 1, 1986. Out of the 14 patients examined, ten were found to shed rotavirus with stools. All strains were characterized for serotype, using a monoclonal antibody-based enzyme-linked immunosorbent assay, and for electropherotype, by polyacrylamide gel electrophoresis of genomic RNA. It was shown that a single serotype 4 (subtype 4A) strain spread within the ward from a primary case to seven other patients. The remaining to patients were found to be infected by a serotype 1 strain that was circulating in the same area prior to the outbreak. The clinical symptoms were unusually severe, since significant dehydration was observed in four of the eight serotype 4 rotavirus-infected children. Previous epidemiological studies had shown that since 1983 serotype 4 strains had not been circulating in Pavia, and the electropherotype of the newly circulating serotype 4 strain was different from those observed in 1981-1983. Thus, the severity of the diarrheal disease appeared to be related to the circulation of both a new serotype and a new electropherotype.