Two-step tuberculin testing of passengers and crew on a commercial airplane.
We investigated the risk of tuberculosis transmission from a person with highly infectious pulmonary tuberculosis to fellow passengers and crew members on a 14-hour commercial flight. The 2-step tuberculin testing was used to minimize the effects of the booster phenomenon. Passengers and flight crew members identified from airline records were contacted by letter, telephone, or both to notify them of their potential exposure to Mycobacterium tuberculosis. The subjects were advised to undergo Mantoux tuberculin skin testing within the required time period to assess a conversion. In addition, information regarding tuberculosis history and other sources of potential exposure was solicited by means of a questionnaire. Of the 277 passengers and crew members on the aircraft, 225 (81.2%) responded. Of these, 173 (76.9%) had positive tuberculin results on the first test (induration > 10 mm). Thirteen subjects with negative results refused further testing; 11 (28%) of the remaining 39 exhibited the booster phenomenon on the second test. Subjects who exhibited the booster phenomenon were significantly more likely to have received previous BCG vaccination. Nine contacts with negative results on the initial test had positive results on a third test administered at 12 weeks after the flight exposure Of these, 6 contacts had previous BCG vaccination, old tuberculosis, or a family member with tuberculosis; the remaining 3 reported on other risk factors for positive reactions. None of these 3 contacts had sat in the same section of the plan as the index patient. The 2-step tuberculin testing procedure is an effective tool for minimization of the booster effect, thus allowing accurate monitoring of subsequent tuberculin conversion rates. Moreover, the clustering of tuberculin skin test conversions among passengers in this study demonstrates the possible risk of M tuberculosis transmission during air travel.