Tuberculosis transmission among five school bus drivers and students in two New York counties

Between November 1994 and April 1995, more than 3300 students in 49 schools in two counties in New York were potentially exposed to five school bus drivers with tuberculosis. This investigation was carried out to determine the extent of transmission of Mycobacterium tuberculosis among students.

Components of the epidemiologic investigation included tuberculin skin-test screening and collection of demographic information for students exposed to a driver with tuberculosis, chest radiography and medical evaluation of individuals with positive skin tests, and DNA fingerprinting of M tuberculosis isolates. A positive skin test was defined as >/=10 mm induration, and a converter was an individual with an increase in reaction size of >/=10 mm in the past 2 years.

The rates of positive skin tests were 0.8%, 0.3%, 9.9%, 1.1%, and 0.7% among US-born students exposed to drivers 1 through 5, respectively. The relative risk for a positive tuberculin skin test was significant only for students exposed to driver 3, and the only secondary case identified among students was exposed to driver 3. The DNA fingerprint patterns of isolates from drivers 3 and 4 matched.

There was no clear evidence of transmission of M tuberculosis to students from drivers 1, 2, 4, or 5. However, evidence suggests that driver 3 transmitted M tuberculosis to students and another driver. Routine annual tuberculin skin-test screening of drivers would not have prevented these tuberculosis exposures.