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Physics department chairman Ken Hayes mon­i­tored humidity levels in some of the physics lecture rooms. Brooke Conrad | Col­legian

People rarely talk about low humidity as a con­tributing factor in the spread of influenza, but the low humidity levels in the U.S. this year may be one of the reasons for the tough flu season.

Research over the past decade shows increased humidity can help prevent the spread of influenza. Assistant Pro­fessor of Biology Silas Johnson said he thinks 40 percent rel­ative humidity is gen­erally accepted as the level above which one can greatly inhibit the spread of the flu.

Aware of this phe­nomenon, physics department chairman Ken Hayes has been checking the humidity levels on the envi­ron­mental mon­itors in a couple of physics lecture rooms.

He said the rel­ative humidity levels, the per­centage of water vapor in the air out of the maximum amount needed for sat­u­ration at that tem­per­ature, has remained at or below 10 percent since the beginning of the semester — sig­nif­i­cantly lower than the minimum 40 percent researchers would rec­ommend.

While the humidity levels in the rooms have been somewhat con­sistent this semester, Hayes noted a vari­ation which occured on Feb. 15, a par­tic­u­larly rainy day.

“I could feel the much higher humidity in the Physics department hallway this morning, and the humidity today in the two lecture rooms was mea­suring 32 percent,” Hayes said in an email that day.

According to Johnson, when a person with influenza coughs or sneezes, he or she gen­erates res­pi­ratory aerosol droplets that carry the flu. With lower humidity, some of the water in the droplets will evap­orate, making the droplets smaller and allowing them to hang longer in the air.

“They can be there for a number of hours,” Johnson said. “If somebody sneezes in an 8 a.m. class and then somebody in a 9 a.m. class comes in, they may get sick because there is still influenza in the tiny little aerosol droplets hanging out in the air.”

With increased humidity, the aerosol droplets are bigger, and it is easier for them to aggregate and settle onto sur­faces. Humidity also causes the virus itself to change; higher humidity can desta­bilize a virus, while lower humidity increases its sta­bility, Johnson said.

Vis­iting Lec­turer of Biology Angie Pytel said she uses a small humid­ifier in her office in the Dow Science Building due to the “chron­i­cally dry” air. She said this has helped reduce her fre­quency of nose­bleeds, and that this problem is not new.

The study of atmos­pheric moisture in relation to the flu is par­tic­u­larly rel­evant this year. According to an article written for Weather Under­ground by Bob Henson, this is because the U.S. is cur­rently expe­ri­encing “one of its worst winters of flu in years” and also its driest winter in more than 30 years.

Even if the rel­ative humidity outside is rather high, it takes less moisture to sat­urate cold air than warm air, according to the article. So on an extremely cold day, it is not dif­ficult to have a high rel­ative humidity and then have this rel­ative humidity drop once the air is heated inside.

Johnson agreed the humidity might be a factor in the par­tic­u­larly bad flu season this year, but he also noted that the strain of flu this year was par­tic­u­larly bad, and the flu vaccine was also not as effective as it has been in past years.

Recent studies show, according to the Center for Disease Control and Pre­vention, that when flu viruses are well-matched to a flu vaccine, the vaccine can reduce the risk of illness by 40 to 60 percent. This winter, in con­trast, the CDC esti­mated that the total vaccine effec­tiveness between Nov. 2 and Feb. 3 was about 36 percent.

“On the humidity question, most of that research has come across maybe in the last 10 years or so,” Johnson said. “There is not a ton of research out there. Maybe a handful of pub­lished sci­en­tific papers. There is an asso­ci­ation that people see, but the actual mech­anism of how that works is still kind of unclear.”

Nev­er­theless, Johnson says the easiest way to inhibit the spread of the flu, even when dealing with low humidity levels, is for people to wash their hands and cover their mouths while sneezing.

“If they are sick, don’t come to class,” Johnson said. “These things will probably do more than raising the humidity levels will.”

Hayes said it would be helpful to start raising awareness on campus about the impor­tance of healthy humidity levels.

“Stu­dents should be aware of this issue and should pay attention to the rel­ative humidity in their living quarters,” he said. “Inex­pensive rel­ative humidity meters are available at stores in town.”