More ventilation may reduce in-flight disease risk

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The risk of catching an infectious illness on commercial aircraft may be reduced if the cabin air is refreshed more frequently, a new report suggests.

“Mathematical modelling of existing epidemiological information suggests that increasing the ventilation rate within the cabin can reduce the risk of infection,” Dr. Mark Gendreau, of the Lahey Clinic Medical Center in Massachusetts told AMN Health.

In the report, published in this week’s issue of the Lancet medical journal, Gendreau and co-author Alexandra Mangili discuss the risk of infectious disease and methods of disease transmission during commercial air travel.

Each year, more than 1 billion men and women travel by air, and 50 million of them travel to developing nations. From the moment these passengers are strapped into their seats and an aircraft begins its ascent, they are exposed to dry humidity, close proximity to strangers and a number of other health risks.

Yet, studies show that the risk of diseases being transmitted from one passenger to another is greatly reduced by ventilation systems within the cabin, according to Gendreau and Mangili.

Much of the air in passenger cabins of commercial aircraft is recirculated, usually through a high efficiency particulate air (HEPA) filter so that any dust, vapors, bacteria, fungi or viral particles can be removed. However, even though most air carriers use them, HEPA filters are not required by the Civil Aviation Authority or the Federal Aviation Administration, the report indicates.

Researchers have not yet determined the risk of disease transmission inside an aircraft. Yet available data, most of which is associated with the in-flight transmission of tuberculosis, suggest that passengers seated within two rows of an affected individual on a flight that lasts more than eight hours have the greatest risk of infection.

At least one exception has been found however, when during an outbreak of severe acute respiratory syndrome (SARS), passengers who sat seven rows away were also affected.

“As the first severe contagious disease of the 21st century, SARS exemplifies the ever-present threat of new infectious diseases and the real potential for rapid spread made possible by the volume and speed of air travel,” the researchers note.

Cabin ventilation may also affect the risk of disease transmission within an aircraft, the report indicates. One exchange of air is known to remove nearly two-thirds of airborne organisms and air is normally exchanged up to 20 times every 60 minutes in airline cabins. In contrast, typical office buildings have only 12 air changes during the same amount of time, the researchers note.

Results from tuberculosis-associated mathematical modelling experiments show that the risk of infection can be reduced by half by simply doubling the rate of ventilation within an aircraft cabin. What’s more, that increased ventilation was shown to nearly eliminate the infection risk of passengers seated 15 seats away from an affected individual.

“Clearly ventilation provides a crucial determinant of risk, and efforts to increase ventilation will reduce risk,” Gendreau and Mangili write.

Overall, the actual risk of infection is less than the perceived risk, Gendreau noted, but travelers should help protect themselves and their fellow passengers by refraining from traveling while sick. They should also follow basic precautions like washing their hands and using an alcohol-based hand sanitizer before eating and after using the bathroom, he said.

Gendreau and Mangili’s review is based on a compilation of findings from previously published studies as well as information obtained from international air carriers and medical representatives from the Civil Air Authority and the Federal Aviation Administration.

SOURCE: Lancet, March 22, 2005

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