Transmission of Mycobacterium tuberculosis among employees in a US government office, Gaborone, Botswana.
A US government office located in Botswana where two office employees, one negative and one positive for the human immunodeficiency virus (HIV), were diagnosed with pulmonary tuberculosis (TB) in January 1998. One employee had been symptomatic with untreated laryngeal TB for 8 months. To determine the extent of and risk factors for TB transmission in the office. Office contacts were interviewed and a tuberculin skin test (TST) was performed. A positive TST was defined as > or = 10 mm induration for employees from countries where TB is highly endemic, and as > or = 5 mm induration for those from low prevalence counties. Of 79 office contacts investigated, 54/57 (94.7%) born in high TB prevalence countries had a positive TST compared with 4/22 (18.2%) from low prevalence countries (RR 5.1, 95% CI 2.1-12.7, P < 0.001). Of 20 US-born contacts, three (15%) had documented TST conversion, two of whom were co-workers of the employee with laryngeal TB. Isolates of Mycobacterium tuberculosis from the TB cases had matching DNA fingerprints. Delayed diagnosis in a setting of high TB prevalence may have contributed to transmission within a US government office located in Botswana. Transmission may have been underestimated due to the high background prevalence of tuberculous infection in the population. Recent tuberculous transmission to persons living with HIV infection may be playing an important role in the escalating TB epidemic in Africa.