Transmission of Mycobacterium tuberculosis among employees in a US Government Office, Gaborone, Botswana

SETTING: A US government office located in Botswana where two office employ ees. one negative and one positive for the human immunodeficiency virus (HI V), were diagnosed with pulmonary tuberculosis (TB) in January 1998. One em ployee had been symptomatic with untreated laryngeal TB for 8 months. OBJECTIVE: To determine the extent of and risk factors for TB transmission in the office, METHODS: Office contacts were interviewed and a tuberculin skin test (TST) was performed. A positive TST was defined as greater than or equal to 10 mm induration for employees from countries where TB is highly endemic and as greater than or equal to 5 mm induration for those h-om low prevalence coun ties. RESULTS: 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 c ontacts, three (15%) had documented TST conversion, two of whom were co-wor kers of the employee with laryngeal TB. Isolates of Mycobacterium tuberculo sis from the TB cases had matching DNA fingerprints. CONCLUSION: Delayed diagnosis in a setting of high TB prevalence may have c ontributed to transmission within a US government office located in Botswan a. transmission may have been underestimated due to the high background pre valence of tuberculous infection in the population. Recent tuberculous tran smission to persons living with HIV infection may be playing an important r ole in the escalating TB epidemic in Africa.