The global influenza pandemic of 1918 was the deadliest in history, claiming the lives of more than 50 million people worldwide. Although the cause of the outbreak has been attributed to infection from the H1N1 virus, a 2008 study co-authored by Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, suggested the primary cause of death among those infected was pneumonia.

Fauci and his colleagues conducted an extensive review of the scientific literature detailing the pathological and bacteriological evidence regarding the pandemic, derived from the findings of more than 8,000 autopsies. Then they examined preserved lung tissue samples from 58 of those autopsies to determine the cause of death.

They found that the death rate followed an age-specific, W-shaped curve, with the highest peaks occurring among infants and elderly people and a slightly lower peak occurring among young adults between the ages of 20 and 40 years old. Examination of the tissue samples revealed that severe acute bacterial pneumonia was present in nearly every case as either the primary pathological feature or coincidental to other features commonly associated with influenza infection, including serious injury to the tissues of the respiratory tract.

The primary pathogens identified in the samples were pneumococci, streptococci, and staphylococci – bacteria that commonly reside in the throat and upper respiratory tract and typically pose no harm. However, the injurious tissue changes that accompanied the primary viral infection created an environment conducive to secondary bacterial infection and subsequent pneumonia. Also present in the samples were Bacillus influenzae, bacteria that often facilitate the infiltration of other pneumonia-causing bacteria.

Taken together, these findings suggest that pandemic preparedness should include the stockpiling of antibiotics and bacterial vaccines.

• Link to full study.