Sense of Smell Can Be Victim of Bout With Flu

If you recently suffered from the flu and have not recovered your sense of smell, you aren’t alone, researchers say.

Some patients complain that they are unable to smell things or to taste food after a bout of influenza. Researchers at the University of Pennsylvania and the University of Connecticut first reported the problem and have been looking into it.

It has also come to the attention of researchers at the University of Cincinnati College of Medicine, where patients who come in for treatment at a center for taste and smell disorders have complained of the malady.

Loss Is Usually Brief

It can happen to people who suffer from flu or upper respiratory infections, said Robert Frank, a University of Cincinnati psychophysicist. It is common for sufferers with colds or the flu to lose their sense of smell--and, as a result, their ability to taste--briefly during the time of the ailment. But, Frank said, some people do not regain their sense of smell for months, or longer.

“These people are seeing us six months after the flu has passed, and they still don’t have their sense of smell,” he said. “We still don’t even know if it’s permanent or not. . . . We don’t know for sure right now, but we think there may be people who permanently lose their sense of smell after this kind of episode.”

After a period of time, some victims report sensing a persistent, strange odor. Researchers have not determined what that means, Frank said.

“There’s some indication in some people we’ve seen that they get this persistent odor,” he said. “We hope that when people report these smells, that’s a start of recovery.”

About 25% of the patients who come to the taste-smell center complaining of a loss of smell have a strain of flu that appears to be the culprit, Frank said.

He said specialists have a theory that the flu viruses may take away the victim’s ability to smell by damaging the olfactory epithelium--the skin on the inside of the nose. But, he said, “We really don’t know what happens.”

University of Cincinnati researchers are preparing an application for a U.S. Department of Health and Human Services public health grant to study the problem. They would like funding to follow the progress of people with the loss-of-smell problem, Frank said.

The work could include taking samples of tissue from inside the noses of victims for analysis to determine whether flu viruses cause damage, he said.

Researchers hope to develop treatment methods. “As it stands right now for a person like this, we really have little idea of what to do,” Frank said.

Victims often complain that they have lost their sense of taste because they cannot taste food. But inability to taste is commonly caused by loss of smell, Frank said. A true loss of taste is rare because three different nerves bring smell information to the brain and it is unusual for all three to malfunction, he said.

Can Be Dangerous

The problem can be dangerous when it prevents people from smelling warning odors such as a natural gas buildup in a house.

“One of the big problems is you can’t smell warning odors. There are a lot of older people who can’t smell the gas so they blow themselves up,” Frank said.

Frank is researching the problem with David Smith, director of the university’s Center for Taste and Smell Disorders. Frank and Smith are not medical doctors, but they have training in physics and biology and specialize in evaluating human sensory systems.

“We still don’t really know what the basic mechanisms are for how you taste and smell,” he said. “We don’t really know what makes certain chemicals important, in terms of how you smell them. In that sense, the study of taste and smell is in its infancy.”