March 10, 2005 -- Sitting next to a sneezing stranger during a cross-country flight may seem like the ideal recipe for transmitting infectious diseases, but a new report shows the perceived risk of infection during air travel may be greater than the actual one.
A review of studies on the in-flight transmission of infectious disease shows that simple measures, such as increasing ventilation within aircraft cabins, can drastically reduce the risk of spreading diseases among those on board.
Researchers say although commercial airlines are suitable environments for spreading disease, the environmental control systems used can remove up to 63% of airborne disease-causing organisms. Computer models indicate that doubling the ventilation rate can cut the risk of infection in half.
The increasing affordability and availability of air travel and mobility of people in recent years has allowed infectious diseases that once took years to spread from continent to continent to move as quickly as a transatlantic flight, as evidenced by the recent rapid spread of the SARS (sudden acute respiratory syndrome) epidemic.
In addition, heightened fears of bioterrorism have also caused health officials to look at the potential of spreading infectious diseases through air travel.
But researchers say few studies have looked at the role of air travel in spreading infectious diseases, and more attention should be paid to this important public health issue.
In the study, which appears in the March 12 issue of The Lancet, researchers reviewed published studies on the transmission of infections diseases during commercial air travel.
They found studies of tuberculosis transmission during air travel show that the risk of disease spreading to other healthy passengers is associated with sitting within two rows of a contagious passenger for a flight longer than eight hours. Researchers say this finding should apply to other infectious diseases that spread through the air, such as colds and flu.
But one outbreak of SARS on board a flight from Hong Kong to Beijing showed that passengers as far away as seven rows from the infected individual were affected.
The review showed that spraying aircraft to kill insects such as mosquitoes seems to be effective in controlling the spread of diseases that spread in this manner, like malaria.
Researchers say health regulations recommend disinfecting aircraft traveling from countries with malaria and other similar disease, but only five countries currently do so (Australia, India, Kiribati, and Uruguay).
The study also showed that the risk of disease transmission within the aircraft cabin seems to be affected by cabin ventilation. One study showed an air exchange removed up to 63% of airborne organisms in that space.
Researchers say use of HEPA (high efficiency particulate air) filters also clearly reduces the risk of transmitting disease. A survey showed that most airlines equip their large aircraft with HEPA filters, but it's not required.
Ticket to Infection?
"Many of us believe air travel is also a lottery ticket for an upper respiratory infection," write David Ozonoff and Lewis Pepper of the Boston University School of Public Health, in an editorial that accompanies the study. "An aeroplane cabin provides the smallest volume of available air per person of any public space."
But they say the study shows that researchers are only beginning to study air travel as a method of spreading infectious diseases.
Ozonoff and Pepper advise that regulations requiring the use of HEPA filters for any airplane that recirculates air should be seriously considered.
But until then, they say advice to air travelers remains generic: "good personal hygiene to protect yourself (wash hands frequently, particularly before eating), cover nose and mouth when sneezing or coughing, and wash hands afterwards to protect others."