"The bacteria most frequently associated with secondary infections after influenza in 1918–1919 were the pneumopathogens Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus. Almost all of the tens of millions of deaths worldwide during the 1918 pandemic were associated with secondary bacterial infections, primarily with Gram-positive bacteria. Had it not been for secondary bacterial pneumonias caused by these and other pneumopathogens, the 1918 pandemic likely would have been associated with a far lower mortality. Increased susceptibility to secondary bacterial pneumonias in persons with influenza should be considered an intrinsic property of influenza virus pathogenicity, and this is likely to be the case for other pathogenic influenza viruses."