A Train Passenger with Pulmonary Tuberculosis: Evidence of Limited Transmission During Travel

Marisa Moore 0 1 Sarah E. Valway 0 1 Walter Ihle 0 1 Ida M. Onorato 0 1 0 Received 19 February 1998; revised 13 August 1998. The investigation was carried out as a public health investigation. Financial support: This work was supported by the Centers for Disease Control and Prevention. Elimination, Centers for Disease Control and Prevention , Mailstop E-10, Atlanta, Georgia 30333 1 From the Epidemic Intelligence Service, Epidemiology Program Office, and the Division of Tuberculosis Elimination, National Center for HIV , STD, and TB Prevention, Centers for Disease Control and Prevention , Atlanta, Georgia In January 1996, smear- and culture-positive tuberculosis (TB) was diagnosed for a 22-year-old black man after he had traveled on two U.S. passenger trains (29.1 hours) and a bus (5.5 hours) over 2 days. To determine if transmission had occurred, passengers and crew were notified of the potential exposure and instructed to undergo a tuberculin skin test (TST). Of the 240 persons who completed screening, 4 (2%) had a documented TST conversion (increase in induration of 10 mm between successive TSTs), 11 (5%) had a single positive TST (10 mm), and 225 (94%) had a negative TST (10 mm). For two persons who underwent conversion, no other risk factors for a conversion were identified other than exposure to the ill passenger during train and/or bus travel. These findings support limited transmission of Mycobacterium tuberculosis from a potentially highly infectious passenger to other persons during extended train and bus travel. - relocated to live with family in November 1995. Shortly thereafter, he became symptomatic with cough. He also reported a several-week history of fever, chills, hemoptysis, and weight loss before his trip. He had not sought medical care until he was aboard the train, when he realized he was too ill to continue his trip. Train officials arranged to have paramedics take him off the train before his destination, and an emergency department evaluation determined that he required hospitalization. There were extensive bilateral cavities on his chest radiograph (figure 1), and his M. tuberculosis isolate was susceptible to firstline anti-TB drugs. Despite anti-TB therapy as an inpatient, however, he died of pulmonary hemorrhage 2 weeks after the train trip. Of two household members exposed from November 1995 through January 1996, one previously had a positive tuberculin skin test (TST), and the other had a documented TST conversion between January and April 1996. Of two visitors to the home for 1 week in January 1996, a 2-year-old child with a positive TST was treated for primary TB on the basis of a clinical diagnosis, and an adult visitor had a negative TST 6 weeks after exposure, although no follow-up testing was done for this patient. The ill passenger had traveled on two U.S. passenger trains (29.1 hours) and one bus (5.5 hours) over 2 days. He was highly infectious on the basis of clinical criteria at diagnosis, and the duration of his train and bus travel during January 1996 was sufficient to pose a potential risk to other passengers and crew members. Given these factors and the lack of information regarding risk of transmission of M. tuberculosis aboard trains, we conducted an investigation involving all passengers and crew members. Methods The passenger with TB was interviewed regarding his symptoms and his seating and movement on the train. The Figure 1. Chest roentgenogram of a train passenger with highly infectious tuberculosis on the day that he was taken off the train in January 1996; the film shows extensive bilateral pulmonary disease with cavitary lesions. train operator was able to provide a list of passengers and crew members; however, the only available contact information was telephone numbers. Passengers and crew members were notified within 2 weeks of the possible exposure during train and/or bus travel via both telephone (to obtain addresses) and certified mail. Because of the point exposure (vs. continuous exposure over weeks to months) and the immediate report of the case to public health officials, we recommended that all persons undergo a baseline two-step TST (i.e., an initial TST and then a second test 1 week later if the initial TST was negative) by the Mantoux method. If both TSTs were negative, then we recommended a final TST 3 months after the trip. For persons with a positive TST, clinical evaluation and follow-up (including administration of preventive therapy if indicated) were conducted by the health department or private health care provider, with consultation provided by the investigators. We requested that a self-administered questionnaire eliciting demographic characteristics, BCG vaccination status, and information on risk factors for TB (e.g., other TB exposures and country of birth) be completed. A form for the health department or a private health care provider to record the TST results was also provided. Follow-up efforts included a reminder letter followed by telephone calls. Persons with a positive TST were interviewed by telephone to review other risks for TB infection and their seat assignment and/or movement on the train. Persons with a prior positive TST and persons taking medication (e.g., cancer chemotherapy and high-dose prednisone therapy) or for whom a medical condition was diagnosed (e.g., HIV infection) whose TST was likely to have a falsenegative result were excluded from analysis. TSTs that were self-read or not read between 48 and 72 hours after being administered were also excluded from analysis. If millimeters of induration were not recorded, the result was read as negative; a negative result was interpreted to be 10 mm. For epidemiological analysis, a positive TST was defined as an induration of 10 mm, and a TST conversion was defined as an increase of 10 mm in the past 2 years. A final TST result was defined as a negative result ( 10 mm) at least 10 weeks after the trip, a positive result, or a conversion. Information about the train cars, the duration of train and bus travel, and boarding and destination points for each passenger were obtained from the train operator. The type of ventilation in the train was reviewed with the train engineering staff. Ventilation studies provided by the operator were also reviewed. Results The person with infectious TB traveled on two trains and one bus. The first train trip was from Chicago to Pittsburgh and was 12.3 hours in duration; because of flooded train tracks, he took a 5.5-hour bus trip (nonstop except for a brief lunch stop) from Pittsburgh to Washington, D.C. The second train trip was from Washington, D.C. to Florida and took 16.8 hours. Each train was composed of coach cars, at least one sleeper car, and at least one dining and/or lounge car. Each train car had its own ventilation system, and the windows did not open in any of the train cars. Air was reported to recirculate in each car through a typical air-conditioning filter with (...truncated)