Efficacy of secondary isoniazid preventive therapy among HIV-infected Southern Africans: time to change policy?

To determine the efficacy of secondary preventive therapy against tuberculosis (TB) among gold miners working in South Africa. An observational study. Health service providing comprehensive care for gold miners. 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). 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 x 106 cells/l, and > or = 200 x 106 cells/l was 5 and 19, respectively. 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.