Most deaths in the 1918 influenza pandemic were due not to the virus alone but to common bacterial infections that took advantage of victims' weakened immune systems, according to two new studies that could change the nation's strategy against the next pandemic.
"We have to realize that it isn't just antivirals that we need," said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases and coauthor of one study. "We need to make sure that we're prepared to treat people with antibiotics," said Fauci, whose study will be released online this month by the Journal of Infectious Diseases.
In both studies, scientists analyzed a trove of historical documents from around the world, examining firsthand accounts, medical records and autopsy reports.
Writing about the 1918 influenza outbreak in the August issue of the journal Emerging Infectious Diseases, researchers reported that few deaths were swift, which is what scientists believed characterized a viral pandemic. Instead, they found most deaths occurred a week to two weeks later -- indicating the deaths were the result of opportunistic bacterial infections.
Most of the bacteria recovered from patients, dead or alive, are common colonizers of the noses and throats of healthy people, according to coauthors Dr. John F. Brundage, a medical epidemiologist at the Armed Forces Health Surveillance Center in Silver Spring, Md., and Dr. G. Dennis Shanks, director of the Australian Army Malaria Institute in Queensland.
Both groups of researchers were trying to understand why the 1918 virus -- a novel strain of influenza for which few people had natural immunity -- was so lethal. The virus swept the globe, killing an estimated 50 million people, striking down young, healthy adults even though influenza usually kills the very young, the elderly and the chronically ill.
It has long been recognized that most flu deaths are due to pneumonia caused by secondary bacterial infections.
But to explain the 1918 pandemic's unusual virulence, many scientists had come to believe the virus killed by provoking an overzealous, destroy-the-village-to-save-it immune response, especially in young adults with robust immune systems.
In a previous experiment, scientists reconstructed the 1918 virus -- using a genetic blueprint pieced together in 2005 from scraps of frozen DNA -- and injected it in mice and monkeys. The animals' immune systems responded violently, inflaming and flooding their lungs with blood and fluids, essentially drowning them.
