According to an analysis published last week, painkillers taken to treat fevers could cause 2,000 flu deaths each year in the United States alone.
Fever is thought to be an antiviral weapon, because many viruses find it hard to replicate at temperatures above the body’s normal 98.6 degrees. But research hasn’t made it clear whether relieving fever slows recovery.
Some studies have shown that lowering fever may prolong viral infections and increase the amount of virus we can pass on to others, says David Earn at McMaster University in Ontario.
To find out what impact this might have on a flu epidemic, Earn and his colleagues turned to a 1982 study that showed that ferrets, a common animal model for human flu, produced more seasonal flu virus if their fevers were lowered either with painkillers or by having their fur shaved off.
Earn’s team used these findings to estimate how much more virus people with ordinary flu might produce if their fevers were suppressed, and the researchers used epidemiological studies in people to estimate how many more cases of flu this might cause.
With the help of a mathematical model, they applied these estimates to the number of Americans each year who get flu, develop fever and take the drugs.
They found that painkillers as used in the United States could be increasing the transmission of ordinary winter flu by up to 5 percent.
Every winter, an average of 41,000 people, most of them elderly, die of flu in the United states. So painkiller use could mean 700 to 2,000 extra deaths per year, depending on the flu strain circulating.
Paul Andrews, a member of the McMaster team, says this estimate is conservative because it factors in only increased amounts of virus shed. Longer shedding time would also make a difference, as would people who feel better with painkillers and return to work or school while still infectious.
Others are more cautious. Nick Phin, head of respiratory diseases at Public Health England, thinks the study relies too much on animal data. He says painkillers are safe and effective against flu.
It is best to avoid using these drugs routinely, however, says Edward Purssell of King’s College London. He was on an official panel in England last year that recommended painkillers in children younger than 5 only to relieve pain. “Fever won’t hurt,” he says, “and it might help.”