Nosocomial transmission of tuberculosis associated with a draining abscess

Nine secondary cases of tuberculosis and 59 tuberculin skin test conversions occurred after exposure to a hospitalized patient with a large tuberculous abscess of the hip and thigh. Among 442 tuberculin-negative hospital employees, the relative risk of skin test conversion associated with recalled exposure to the patient was 14.0 (95% confidence limits, 6.8, 28.7). Four of 5 surgical suite employees who assisted with incision and debridement of the abscess had skin test conversions, as did 85% of 33 employees on a general medical floor who recalled exposure to the patient and 30% of 20 intensive care unit employees who recalled exposure. The prevalence of tuberculin reactivity in visitors and other patients on two floors also showed a strong association with exposure to the patient. A high concentration of Mycobacterium tuberculosis in the abscessed tissue, disturbance of the surface of liquid drainage from the abscess by irrigations and by the agitated behavior of the patient, and positive air pressure in the patient's room are factors that appear to have contributed to the high risk of tuberculosis transmission.