Transmission of multidrug-resistant and extensively drug-resistant tuberculosis in a metropolitan city

Eric Chung Ching Leung, Chi Chiu Leung, Kai Man Kam, Wing Wai Yew, Kwok Chiu Chang, Wai Man Leung, Cheuk Ming Tam


Multidrug-resistant (MDR)- tuberculosis (TB) and extensively drug resistant (XDR)-TB reportedly lead to increased household transmission.

This is a retrospective cohort study of active TB occurring among household contacts exposed to MDR-TB.

Of 704 contacts in 246 households, initial screening identified 12 (1.7%) TB cases (prevalent cases) and 17 (2.4%) contacts that subsequently developed active TB (secondary cases) after a median (range) duration of 17 (5–62.5) months. Eight prevalent cases and three secondary cases had MDR-TB. TB incidence rates per 100 000 person-years were 254.9 overall and 45.0 for MDR-TB. XDR-TB in the index MDR-TB patient significantly increased the odds of identifying a prevalent TB case to 4.8 (95% CI 1.02–22.5), and the hazard of finding a secondary TB case to 4.7 (95% CI 1.7–13.5). Molecular fingerprinting confirmed household transmission of MDR-TB. Of 20 retrievable isolates from 27 XDR-TB index cases, restriction fragment length polymorphism analysis showed clustering among 13 (65%), with 11 (55%) due to recent transmission by n-1 method and an identifiable household source in only three (27.2%) of the 11 cases.

XDR-TB relative to MDR-TB significantly increases household transmission of TB, probably reflecting prolonged/higher infectivity, and indicating a need for prolonged household surveillance. XDR-TB may largely transmit outside of the household settings.


  • Statement of Interest

    None declared.

  • Received May 4, 2012.
  • Accepted June 27, 2012.
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