Clinical data have shown that the majority of deaths  following influenza infection are due to secondary bacterial pneumonia superinfection during influenza pandemics. More than 90% of lung culture samples from autopsy records during 1918 pandemics were positive for bacteria, including Streptococcus pneumonia, Staphylococcus aureus, and Haemophilus influenza. Streptococcus was the most common pathogen and responsible for over 50% of the deaths.