Patterns of viral respiratory tract infections in Singapore.

A second retrospective study on viral respiratory tract infections, based on 12 years' laboratory reports for the influenza viruses, and 9 years' reports for the other respiratory viruses was made. Seasonal variation in incidence was found to occur with infections due to the influenza viruses, respiratory syncytial virus, and parainfluenzavirus type 1. Observations made previously on the age distribution of specific respiratory viral infections, and the association of the viruses with various respiratory syndromes were generally confirmed.