SETTING: Multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) are now a nationwide epidemic in South Africa. Epidemiological data suggest nosocomial transmission as the primary route of spread; however, transmission among household contacts has not yet been investigated. OBJECTIVE: To determine the incidence rates of MDR- and XDR-TB among household contacts of MDR- and XDR-TB index cases diagnosed between January 2005 and September 2008 in a high human immunodeficiency virus prevalence setting. DESIGN: Prospective, observational study evaluating adult household contacts for active TB by culture and drug susceptibility testing at index case diagnosis and again 1 year later. Outcomes were incidence and time to diagnosis of MDR- and XDR-TB. RESULTS: A total of 1766 contacts of 221 MDR-TB and 287 XDR-TB index cases were screened. Of 793 contacts of MDR-TB index cases, 14 (1.8%) were diagnosed with MDR-TB (incidence 1765/100 000); 19 (2.0%) of 973 XDR-TB contacts had XDR-TB (incidence 1952/100 000). Median time to diagnosis of household cases was 70 days (interquartile range 57-89). CONCLUSION: Incidence rates of MDR- and XDR-TB among household contacts were extremely high, with most secondary cases occurring shortly after the diagnosis of the index case. Active case finding of drug-resistant TB is a high-yield public health activity and must be a priority, as early diagnosis may stem further disease spread and improve survival.
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