RSV is an important respiratory pathogen in infants. There is increasing evidence that it also plays a significant role in seasonal morbidity of the elderly and those with underlying cardiopulmonary disease. This study followed two “at risk” populations for up to two winter seasons: a cohort of healthy elderly subjects (>65 years: n = 216 (year 1), n = 289 (year 2)) and adults with cardiopulmonary disease (n = 204 (year 1), n = 265 (year 2)). A third group of 625 patients admitted acutely into hospital with respiratory symptoms and who were also in either of these “at risk” groups was also studied. A PCR positive swab, detection of RSV in cell culture, or a fourfold rise in serum IgG to RSV envelope glycoproteins was taken as evidence of RSV infection. Overall, 130 RSV infections were identified over 2 years: 61 in the hospitalised group, 32 in the healthy elderly subjects, and 37 in those with cardiopulmonary disease. A multivariate analysis revealed that age <65 years, poor baseline functional status, and low initial titres of protective RSV neutralising antibody were independently associated with RSV related hospitalisation. There was a non-significant trend for an effect of chronic pulmonary disease. Neutralising antibody levels to RSV were lower in the hospitalised group.

These data suggest that inadequate humoral immunity is an independent risk factor for hospitalisation during RSV infection in at risk populations, and that these groups might benefit most from protective vaccination.