The number of patients with bacterial pneumonia diagnosed between 30 days before and 30 days after the date of influenza diagnosis, which was designated as the index date (day 0). Pre-influenza pneumonia, concomitant pneumonia, and secondary pneumonia were defined as bacterial pneumonia diagnosed between 30 and 4 days before the index date, between 3 days before and 6 days after the index date, and between 7 and 30 days after the index date, respectively.