Proportion of tuberculosis transmission that takes place in households in a high-incidence area.

The prevalence of infection among household contacts of people with tuberculosis is high. This information frequently guides active case finding. We analysed DNA fingerprints of Mycobacterium tuberculosis from 765 tuberculosis patients in Ravensmead and Uitsig, adjacent suburbs of Cape Town, South Africa. In 129 households in which DNA fingerprints were available for more than one patient, we identified 313 patients, of whom 145 (46%) had a fingerprint pattern matching that of another member of the household. The proportion of transmission in the community that took place in the household was 19%, and therefore, in this high-incidence area, tuberculosis transmission occurs mainly outside the household.