[Exposure to Mycobacterium tuberculosis during a bus travel]

In an outbreak of tuberculosis that occurred in a school, we evaluated the possible transmission during a trip in a school bus as the cause of infection. SUBJECTS, PATIENTS AND METHODS: Contact tracing of the driver, 3 teachers and 49 students from different grades who were travelling from Málaga to Sierra Nevada (Spain) in March 1998. All the students from the ten grades where any case of tuberculosis appeared from April to December 1998 and all the teachers of the school were included.

At the school, 232 students were studied. The prevalence of the infection was 35%. A total of 12 new cases among the students were found. No teachers out of the 127 examined became ill. Out of the people who travelled by school bus, 2 teachers and 19 students were infected, prevalence among students 46%; five of those become ill. The odds ratio of infection for those having a class mate with positive smears was 5,5. On the other hand, the trip by bus (compared with those who did not take it) meant a odds ratio of 3,4. Most of the infected travellers were sitting in the bus close to the index case.

In this tuberculosis outbreak some of the students who became ill or infected were not near the index case nor friendly with him at class. Therefore is possible that in some cases tuberculosis was transmitted inside the bus.