ABSTRACT
The population-based cohort study on the epidemiology of respiratory syncytial virus (RSV)-associated lower respiratory tract infection (LRI) (RSV-LRI) was conducted in Takhli district from November 1998 to February 2001. The incidence of RSV-LRI was 12.6/1,000 child-year and 5.8/ 1,000 child-year during the first and second year, respectively. RSV accounted for 35.8 per cent of all LRI cases during the first year and significantly decreased to 17.5 per cent during the second year. Three-quarters of RSV-LRI occurred among children under 2 years old (76.6% during the first year and 62.2% during the second year). Most of RSV-LRI in both years occurred from July to October. Risk factor for morbidity of RSV infections were age less than or equal to 2 years (OR = 2.38, 95% CI = 1.22-4.67 p = 0.009) and sleeping with more than 3 persons in the patient's bedroom (OR = 2.92,95% CI = 1.42-6.00, p = 0.002). Most RSV-LRI (63.9%) were clinically diagnosed as having pneumonia. No RSV-LRI deaths were detected. During the first year, RSV subtype B was predominate, in contrast to the second year when subtype A was more predominate. Further research to determine the annual change in subtype of RSV-LRI and correlation of severity of disease with specific subtypes needs to conducted in order to prepare for the future introduction of a vaccine.