When you've got the flu, it can't hurt to take an aspirin or an ibuprofen to control the fever and make you feel better, right? Wrong, some scientists say. Lowering your body temperature may make the virus replicate faster and increase the risk that you transmit it to others. A new study claims that there are at least 700 extra influenza deaths in the United States every year because people suppress their fever.
As a result, if you have the flu and you're taking medication "it may actually be more important that you stay at home because you could be a greater risk to others," says David Earn, a mathematician at McMaster University in Hamilton, Canada, and one of the authors of the paper. Some scientists call that claim premature, however.
The debate about whether treating fever is good or bad for patients has been simmering for decades. Humans have reduced fevers for thousands of years; Hippocrates recommended extracts of the willow tree bark, which was later found to contain salicylic acid, better known as aspirin; Romans, Chinese, and Native Americans used other plants containing similar compounds. But some research conducted in the 1970s suggested that fever may actually be beneficial when you're sick—perhaps because it makes it more difficult for pathogens to multiply—and that cooling your body can have negative consequences.
A 1975 paper in the Journal of the American Medical Association, for instance, showed that people infected with a common cold virus called the rhinovirus shed more virus particles if they were treated with aspirin than untreated patients . Another study found more virus in the noses of ferrets infected with flu if they had been shaved—which reduces their body temperature—or treated with antipyretics , fever-lowering drugs.
The new paper does not add experimental evidence; instead, the authors have for the first time tried to model what fever suppression could mean for an entire population. They estimated how much more virus flu patients shed when they suppress their fever and how much more infectious that makes them; then they combined these numbers with data about the use of antipyretic drugs by parents, patients, and nurses. They conclude that current antipyretic use in the United States leads to at least 1% more flu cases, resulting in 700 extra deaths. The size of the effect depends on how easily the particular strain of the flu is transmitted, however. If the virus is harder to transmit, suppressing fevers could lead to as much as 5% more cases and 2000 more deaths , the researchers report online today in the Proceedings of the Royal Society B.
"The conclusion is not unreasonable," says Philip Mackowiak of the University of Maryland School of Medicine in Baltimore, who has researched fever for decades. But he cautions that the model "involves a tremendous number of assumptions that are only loosely supported by medical literature." For instance, the conjecture that treating fever increases shedding of influenza virus rests solely on the ferret study. "Ferrets may be the best model for influenza, but ferrets in cages treated with antipyretics are very different from human populations," he says. And shedding more virus does not necessarily mean people are more infectious, adds Gérard Krause, an epidemiologist at the Helmholtz Centre for Infection Research in Braunschweig, Germany. "It's plausible but by no means proven."
"Based on this paper you cannot conclude that treating people with fever-lowering medications is a bad idea," adds Walter Haas, an epidemiologist at the Robert Koch Institute in Berlin. The assumption that suppressing fever increases infectivity is built into the model, he says, "so it's no surprise that that is what they come up with at the end."
Earn says he and his colleagues considered the various uncertainties and took care to be as conservative as possible in their estimates; they didn't even include the effect that after an aspirin, people may be more likely to go out and meet people, increasing chances of spreading disease. The main message, he says, is that the effects of suppressing fever need to be studied much more carefully.
That's something everybody can agree on. "It's shocking that we don't know more about the benefits versus the adverse effects of fever on higher animals," Mackowiak says. And Krause finds the paper "inspiring" because it takes the debate about fever suppression from the individual to the population level, which he hadn't given much thought so far himself.
But what does all of this mean for you when you come down with flu this winter? The decision on whether to take antipyretics is up to you, Earn says. Just be aware that your decision may affect other people as well.