SEASONAL TRENDS OF VIRAL RESPIRATORY-TRACT INFECTIONS IN THE TROPICS

To evaluate the seasonal trends of viral respiratory tract infections in a tropical environment, a retrospective survey of laboratory virus isolation, serology and immunofluorescence microscopy in two large gen eral hospitals in Singapore between September 1990 and September 1994 was carried out. Respiratory tract viral outbreaks, particularly among infants who required hospitalization, were found to be associated mai nly with respiratory syncytial (RSV) infections (72%), influenza (11%) and parainfluenza viruses (11%). Consistent seasonal variations in vi ral infections were observed only with RSV (March-August) and influenz a A virus (peaks in June, December-January). The RSV trends were assoc iated with higher environmental temperature, lower relative humidity a nd higher maximal day-to-day temperature variation. Although the influ enza A outbreaks were not associated with meteorological factors, infl uenza B isolates were positively associated with rainfall. These data support the existence of seasonal trends of viral respiratory tract in fections in the tropics.