New research from the National Institute of Allergy and Infectious Diseases (NIAID) has revealed that most deaths during the influenza pandemic of 1918-1919 were not caused by the influenza virus alone, but by bacterial pneumonia that followed the destruction caused by the flu.

Most victims succumbed to pneumonia caused when bacteria that normally inhabit the nose and throat invaded the lungs along a pathway created when the flu virus destroyed the cells that line the bronchial tubes and lungs.

“In essence, the virus landed the first blow while bacteria delivered the knockout punch,” says Anthony S. Fauci MD, NIAD director.
The researchers microscopically examined lung tissue samples from soldiers who died of influenza in 1918 and 1919. The examination found evidence that the virus destroyed the cells lining the bronchial tubes. This loss made other kinds of cells throughout the entire respiratory tract vulnerable to attack by bacteria that migrated down the newly created pathway from the nose to the throat.

Authors of the study warn that a future influenza pandemic could develop in a comparable way. “Preparations for diagnosing, treating, and preventing bacterial pneumonia should be among highest priorities in influenza pandemic planning,” write the authors.
“We are encouraged by the fact that pandemic planners are already considering and implementing some of these actions,” says Fauci.

The Journal of Infectious Diseases published the full study.