Travelers' advisory on tuberculosis.

A hacking cough may prove more than a mere annoyance on a crowded airplane. Health authorities have now described the first case in which an airline passenger with Mycobacterium tuberculosis passed this nasty bug on to some of her fellow passengers.

The transmission of M. tuberculosis occurred during an 8-hour, 38-minute flight from Chicago to Honolulu. The state and federal health investigation focused on a female passenger with full- fledged tuberculosis (TB) who died just weeks after that flight.

The March 3 Morbidity and Mortality Weekly Report (MMWR) indicates that four passengers became infected during that flight. All four sat in the same section of the plane as the woman with TB, who had been coughing. They presumably caught the bug by inhaling tiny, infectious droplets circulating in the air, says Kenneth G. Castro, director of the Division of Tuberculosis Elimination at the Centers for Disease Control and Prevention (CDC) in Atlanta.

Last year, CDC documented a case in which a flight attendant with tuberculosis had infected other crew members (SN: 10/15/94, p.255). That probe failed to show transmission to any passengers on the flights in question. Yet airlines do not routinely keep track of customers after they step off the jetway--a fact that hinders such investigations, Castro points out.

Health officials downplay the risk of catching TB on a crowded flight. "The risk for M. tuberculosis transmission on an aircraft does not appear to be greater than in other confined spaces," the MMWR report says.

"Theoretically, any time you have a combination of someone who's infectious with tuberculosis and exposure that lasts several hours- -then there's a possibility that others will become infected," Castro says. Generally, only people with untreated, full-blown tuberculosis can transmit this microbe, he says. However, even with prolonged exposure, some people never become infected.

People with contagious tuberculosis should not travel commercially, the CDC advises. If an airline finds out that a passenger with TB has been on a flight lasting more than 8 hours, it should notify the other passengers and flight crew.

People concerned about a possible TB exposure can get a skin test from their doctor. If that test is positive, drug treatment can stop a simmering infection from developing into disease, Castro notes.