Infectiousness of a university student with laryngeal and cavitary tuberculosis. Investigative team

A search for the source of infection for four children with tuberculosis (TB) identified a university student with cavitary and laryngeal TB. An investigation was conducted at the university, including tuberculin skin test (TST) screening and the use of questionnaires, chest radiographs, and DNA fingerprint analyses of Mycobacterium tuberculosis isolates. Six students with active TB were identified. All were linked to the source case. TSTs were positive for 22.4% of 419 students who had contact with the source case vs. 3.6% of 1,306 students without contact. The odds of a positive TST increased to 9.0 with 80 hours of classroom contact. Infectiousness increased significantly in the last of three semesters during which the source case was symptomatic (RR of a positive TST in classmates, 4.8; 95% CI, 1.8-11.8). TST conversions were documented in 23 students; eight had, at most, 5 hours of classroom contact. The source case was highly infectious; transmission following only a few hours of exposure was documented. Her infectiousness increased as her clinical course progressed. This report illustrates the potential infectiousness of TB cases and demonstrates important aspects of tuberculosis control.