Trends for invasive pneumococcal pneumonia, virus, and climate data for 1998–99 (A) and 2003–04 (B), United States. IPP, invasive pneumococcal disease; influenza percent, percentage of influenza virus–positive isolates out of all influenza specimens; RSV, respiratory syncytial virus; RSV percent, percentage of RSV-positive isolates out of all RSV specimens.