Background: South Korea is an intermediate TB burden country with a high incidence rate of rifampin-resistant TB (RR-TB). The effect of tuberculosis (TB) preventive treatment (TPT) on household contacts (HHC) of RR-TB in an intermediate TB burden country has not been well evaluated.

Study Design and Methods: This retrospective cohort study analyzed data of HHC investigations from January 2015 to December 2018 in a linked database of the nationwide TB registry and healthcare administrative database of South Korea. The primary outcome was a risk of active TB in HHCs of RR-TB patients following tuberculosis preventive treatment.

Results: Out of 82,783 HHCs with data on drug resistance patterns of the index case, 2,593 (4.6%) were in contact with RR-TB patients. Of these 2,593 RR-TB HHCs, 926 (35.7%) were confirmed to have latent TB infection. Among 926 of LTBI patients, 294 (31.7%) had initiated conventional TPT including isoniazid or rifampin, and 168 (57.1%) had completed it. There was no significant difference in the risk of active TB between the TPT complete group and the LTBI-negative group (aHR, 2.27 [95% CI, 0.58-8.83]). In terms of drug resistance profile concordance, 58.7% of the RR-TB HHCs had a concordant drug resistance pattern with the index cases.

Conclusion:  TB preventive treatment regimens including isoniazid or rifampin effectively prevent TB in household contacts of RR-TB in an intermediate TB burden country. Nationwide HHC investigation combined with TPT may be an effective strategy in reducing TB transmission in intermittent TB burden countries.