METHODOLOGY: A retrospective review was performed of LRTI patients aged less than 24 months who were admitted to the University Malaya Medical Centre between 1982 and 1997. Respiratory viruses in their nasopharyngeal secretion were identified by indirect immunofluorescence, viral culture, or both.

RESULTS: A total of 5691 children were included in the study. The mean age was 8.6 +/- 6.6 months and the M:F ratio was 1.6:1. The most common diagnosis was pneumonia (52%) followed by bronchiolitis (45%) and croup (2%). Positive viral isolation rate was 22.0%. Respiratory syncytial virus (RSV) was the commonest virus isolated (84%), followed by parainfluenza virus (8%), influenza virus (6%) and adenovirus (2%). Patients with positive virus isolation were younger (7.8 +/- 6.2 vs 8.7 +/- 6.7 months, P = 0.0001) and were more likely to have bronchiolitis.