Concerned that ventilation systems for airline cabins might contribute to the spread of contagious diseases, federal health officials are investigating whether some passengers with tuberculosis have infected fellow passengers on long flights.
One federal study, begun this month, seeks to track down and examine all passengers aboard two flights in March, one domestic and one international, each of which had a passenger with active tuberculosis.
A second new study seeks to examine the circumstances under which at least one flight attendant on a separate flight acquired the disease.
Health officials were informed of the cases by state health departments. The officials said the data still are being collected and hadn’t been fully analyzed.
“We have been very much concerned with the transmission of respiratory diseases in airlines,” said Dr. Walter Dowdle, deputy director of the Centers for Disease Control and Prevention in Atlanta, which is conducting the studies.
Dowdle said the two studies are the first that CDC has undertaken about the possible transmission of tuberculosis in airliners, where cabin air is recirculated. The agency previously had studied other infectious diseases that probably were transmitted as a result of poor airliner ventilation.
Tuberculosis is a bacterial disease that is spread through the air by patients in the active stage of the disease. It caused 3 million deaths worldwide last year and infected 8 million more. Health officials say that worldwide one person in three is infected, although in the vast majority of those cases the disease is latent and cannot be transmitted.
Dr. Mark Miller, a public health physician in charge of the first tuberculosis study, said in an interview, “An airline cabin is a closed, confined space, and we’re trying to determine what the risk factors are.” He added, “We make the assumption that the more frequent the air exchange, the better it is for not acquiring tuberculosis.”
To save money cooling the air, which comes into ventilation systems through the engines, airlines in the United States are circulating less fresh air into the cabins of newer planes. Older aircraft built before the mid-1980s provided cabins with 100 percent fresh air that was circulated every three minutes, a rate far greater than that required in the hospital isolation wards where tuberculosis patients are treated.
But the newer models provide only 50 percent fresh air and 50 percent recirculated air that is freshened up to every seven minutes, and sometimes longer. That is less than the rate of air exchange prescribed for hospital TB wards.
