Invasive pneumococcal pneumonia and respiratory virus co-infections.

To confirm whether respiratory virus infections increase susceptibility to invasive pneumococcal pneumonia, we examined data from 11 influenza seasons (1994-2005) in the United States. Invasive pneumococcal pneumonia was significantly associated with influenza and respiratory syncytial virus activities in 5 seasons. Association strength was higher when strain H3N2 was the predominant influenza A virus strain.