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High incidence of latent tuberculous infection among South African health workers: an urgent call for action.

SETTING
In South Africa, health care workers (HCWs) are at two-fold greater risk of acquiring tuberculosis (TB) disease than the general population. Few studies have evaluated the risk of incident tuberculous infection.


OBJECTIVE
To determine the incidence and risk factors for latent tuberculous infection (LTBI) among HCWs and to compare the results of the interferon-gamma release assay (IGRA) with those of the tuberculin skin test (TST).


DESIGN
HCWs, including medical students, underwent a TST and human immunodeficiency virus (HIV) and IGRA testing at baseline and 12 months, and IGRA at 6 months. The participants kept 12-month TB exposure logs.


RESULTS
Among 199 participants (150 [76%] females, median age 31 years [range 20-61]), incident LTBI was documented using IGRA in 25/97 (26%; incident rate 29 cases/100 person-years [py], 95%CI 20-44) and using TST in 25/93 (27%; incident rate 29 cases/100 py, 95%CI 19-42). Agreement between TST and IGRA was poor (44.8%, κ = 0.23). Higher annual exposure to TB cases was reported among persons with LTBI than in those who were persistently IGRA-negative (81 cases, 95%CI 61-102 vs. 50 cases, 95%CI 43-57, P < 0.01).


CONCLUSION
The high LTBI incidence and the association of incident LTBI with annual TB caseload among HCWs indicate that more effective TB infection control should be implemented in South African health care facilities.