Thibela TB: design and methods of a cluster randomised trial of the effect of community-wide isoniazid preventive therapy on tuberculosis amongst gold miners in South Africa.

BACKGROUND: South Africa has the third highest annual number of new tuberculosis (TB) cases globally. The resurgence of TB which has particularly affected gold miners in South Africa, is attributed to occupational risk factors for TB including silica dust exposure and high HIV prevalence. Isoniazid preventive therapy (IPT) is recommended for individuals at high risk to prevent both HIV-related TB and silicotuberculosis, but global uptake has been poor. We describe the design of a cluster randomised study, "Thibela TB", which compares routine IPT targeted to those identified as at higher risk of TB (due to HIV infection or silicosis) against a "community-wide" approach in which IPT is offered to all employees. The trial is registered with the Current Controlled Trials: Registration number ISRCTN63327174. METHODS: We describe the rationale for the intervention of community-wide IPT, drawing on studies conducted in 1950-1960s in the pre-HIV era. The design of the study, including the definition of the cluster, is presented and advantages and limitations of such a design are discussed. CONCLUSION: If successful in reducing TB incidence and prevalence, this trial has potential to make a major contribution to TB control policy in high HIV settings, providing evidence concerning efficacy, and additionally safety and population-level effects on drug susceptibility patterns. Such rigorous evaluation is essential to provide policy makers with an evidence base to guide community-level TB prevention strategies.