Objectives. During the winter months there is a remarkable increase in paediatric hospitalisations due to viral acute lower respiratory infections (ALRI). We aimed to perform a five-year retrospective analysis (1998–2002) of ALRI viral aetiology in children under 5 years of age admitted to public hospitals in Buenos Aires city to evaluate its seasonality.

Materials and methods. Nasopharyngeal aspirates (NPA) were analysed by indirect immunofluorescence to determine viral aetiology. A Spearman's rank correlation test between meteorological parameters and viral frequencies was performed.

Results. Viruses were identified in 6083 (32.8%) of 18561 NPA tested. Among the former 4796 (78.8%) were RSV, 508 (8.3%) IA, 473 (7.8%) AV, 293 (4.8%) PIV and 13 (0.2%) IB. RSV and IA peaked during the coldest and dampest months, whereas PIV did so in early spring and AV lasted throughout the year. For RSV and IA an inverse correlation with mean monthly temperature (r=−0.9 and r=−0.87, respectively, p<0.0001) and solar UVB radiation (r=−0.92 and r=−0.80, respectively, p<0.0001) was detected, while it was positive when relative humidity was considered (r=0.6, p<0.0001 and r=0.47, p=0.0068, respectively).

Conclusions. This study highlights the seasonal variation of ALRI and allows the implementation of adequate healthcare strategies and practice guidelines.