Efficacy of secondary isoniazid preventive therapy among HIV-infected Southern Africans

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Abstract
Objective: To determine the efficacy of secondary preventive therapy against tuberculosis (TB) among gold miners working in South Africa. Design: An observational study. Setting: Health service providing comprehensive care for gold miners. Methods: The incidence of recurrent TB was compared between two cohorts of HIV-infected miners: one cohort (n = 338) had received secondary preventive therapy with isoniazid (IPT) and the other had not (n = 221). Results: The overall incidence of recurrent TB was reduced by 55% among men who received IPT compared with those who did not (incidence rates 8.6 and 19.1 per 100 person-years, respectively; incidence rate ratio, 0.45; 95% confidence interval 0.26–0.78). The efficacy of isoniazid preventive therapy was unchanged after controlling for CD4 cell count and age. The number of person-years of IPT required to prevent one case of recurrent TB among individuals with a CD4 cell count < 200 × 106 cells/l, and ≥ 200 × 106 cells/l was 5 and 19, respectively. Conclusion: Secondary preventive therapy reduces TB recurrence: the absolute impact appears to be greatest among individuals with low CD4 cell counts. International TB preventive therapy guidelines for HIV-infected individuals need to be expanded to include recommendations for secondary preventive therapy in settings where TB prevalence is high.