Setting: Domestic and international air-flights.
Objective: To estimate the risk of tuberculosis (TB) transmission aboard aircraft.
Design: A contact investigation of passengers and crew from two flights was conducted following identification of a fellow passenger with pulmonary TB. Immediate post-exposure and follow-up tuberculin skin tests (TSTs) were obtained.
Results: Of 120 contacts, 86 (72%) had a negative TST (< 5 mm); 29 (24%) a positive TST (> or = 5 mm), and 5 (4%) a TST conversion. Of the 29 persons with a positive TST, 27 had other identified risk factors for TB. Risk factors for positive TST included non-US birth (Relative Risk (RR) 9.7 P < 0.01) or history of Bacille Calmette-Guérin (BCG) vaccination (RR undefined; P < 0.01). Risk was not associated with specific aircraft or seat relative to the index case for US-born contacts. All five TST converters were born in countries where BCG vaccine is routinely given.
Conclusion: The positive TST reactions and conversions suggest boosting from BCG vaccination or prior exposure in TB-endemic countries. Since two positive contacts had no other identified risk factor, TB transmission on board the aircraft could not be excluded. Contact investigation of exposed aircraft passengers should be considered on a case-by-case basis, with consideration of the infectiousness of the ill passenger and the flight circumstances.