London, Aug 5 : A new study has concluded that bacteria, not influenza viruses, killed most people in the 1918 flu epidemic.
For the study, John Brundage, a medical microbiologist at the Armed Forces Health Surveillance Center in Silver Spring, Maryland, and his team sifted through first-hand accounts, medical records, and infection patterns from 1918 and 1919.
They concluded that although a nasty strain of flu virus swept around the world, bacterial pneumonia that came on the heels of mostly mild cases of flu killed the majority of the 20 to 100 million victims of the so-called Spanish flu.
"We agree completely that bacterial pneumonia played a major role in the mortality of the 1918 pandemic," New Scientist quoted Anthony Fauci, director of National Institute for Allergy and Infectious Disease in Bethesda, Maryland, as saying.
Jonathan McCullers, an expert on influenza-bacteria co-infections at St Jude Children's Research Hospital in Memphis, Tennessee, said that this is not to say that flu viruses do nothing.
McCullers' study suggests that influenza kills cells in the respiratory tract, providing food and a home for invading bacteria.
On top of this, an overstressed immune system makes it easier for the bacteria to get a foothold.
However, the shear carnage of 1918 caused many microbiologists to reconsider the role of bacteria, and some pointed their fingers firmly at the virus.
When US government scientists resurrected the 1918 strain in 2005, the virus demolished cells grown in a Petri dish and felled mice by the dozen.
"The 1918 pandemic is considered to be - and clearly is - something unique, and it's widely understood to be the most lethal natural event that has occurred in recent human history," Brundage said.
However, to reassess this conclusion, he and co-author Dennis Shanks, of the Australian Army Malaria Institute in Enoggera, Queensland, scoured literature and medical records from 1918 and 1919.
The more they investigated, the more bacteria emerged as the true killers, an idea now supported by most influenza experts.
For instance, had a super virus been responsible for most deaths, one might expect people to die fairly rapidly, or at least for most cases to follow a similar progression.
However, Shanks and Brundage found that few people died within three days of showing symptoms, while most people lasted more than a week, some survived two - all hallmarks of pneumonia.
Military health records for barracks and battleships also painted a different picture.
Researchers found that new recruits, men unlikely to have been exposed to resident bacteria, died in droves, while soldiers whose immune systems were accustomed to the local bugs survived.
Brundage said that the most compelling medical experts of the day identified pneumonia as the cause of most deaths.
"The bottom line is we think the influenza virus itself was necessary - but not sufficient - to cause most of the deaths," he said.
Brundage said that government efforts to gird for the next influenza pandemic, bird flu or otherwise, ought to take notice and stock up on antibiotics.
The study was published in Emerging Infectious Disease.