Mortality attributable to 9 common infections: significant effect of influenza A, respiratory syncytial virus, influenza B, norovirus, and parainfluenza in elderly persons

BACKGROUND: Because there may be substantial hidden mortality caused by common seasonal pathogens, we estimated the number of deaths in elderly persons attributable to viruses and bacteria for which robust weekly laboratory surveillance data were available.

METHODS: On weekly time series (1999-2007) we used regression models to associate total death counts in individuals aged 65-74, 75-84, and ≥85 years (a population of 2.5 million) with pathogen circulation-influenza A (season-specific), influenza B, respiratory syncytial virus (RSV), parainfluenza, enterovirus, rotavirus, norovirus, Campylobacter, and Salmonella-adjusted for extreme outdoor temperatures.

RESULTS: Influenza A and RSV were significantly (P < .05) associated with mortality in all studied age groups; influenza B and parainfluenza were additionally associated in those aged ≥75 years, and norovirus was additionally associated in those aged ≥85 years. The proportions of deaths attributable to seasonal viruses were 6.8% (≥85 years), 4.4% (75-84 years), and 1.4% (65-74 years), but with great variations between years. Influenza occasionally showed lower impact than some of the other viruses.

CONCLUSIONS: The number of different pathogens associated with mortality in the older population increases with increasing age. Besides influenza A and RSV, influenza B, parainfluenza and norovirus may also contribute substantially to elderly mortality.