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 general 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 mainly with respiratory syncytial
(RSV) infections
(72%), influenza (11%) and parainfluenza viruses (11%). Consistent seasonal
variations in
viral infections were observed only with RSV (March–August) and influenza
A virus (peaks in
June, December–January). The RSV trends were associated with higher
environmental
temperature, lower relative humidity and higher maximal day-to-day temperature
variation.
Although the influenza A outbreaks were not associated with meteorological
factors, influenza
B isolates were positively associated with rainfall. These data
support the existence of seasonal
trends of viral respiratory tract infections in the tropics.