Transmission of multiple drug-resistant tuberculosis: report of a school and community outbreak.

An outbreak of tuberculosis in 1976 was caused by mycobacteria resistant to isoniazid (INH), streptomycin (SM), and para-aminosalicylic acid (PAS). High rates of infection associated with exposure to the index case suggested that transmission of resistant organisms had occurred, and the subsequent appearance of bacteriologically proven INH-SM-PAS-resistant tuberculosis in four school contacts of the index case confirmed this fact. Retrospective investigation revealed that the school outbreak was part of an ongoing community outbreak dating back at least to 1964. Through the use of case histories, drug-susceptibility patterns, and phage typing, 15 documented and seven presumed INH-SM-PAS-resistant, epidemiologically linked cases were found; two of these persons died of tuberculosis. Six additional cases with INH-SM-PAS resistance that could not be epidemiologically linked to the outbreak were also identified. The potential of drug-resistant strains for causing disease in humans should not underestimated.