 A key TB control strategy is therapy of latent TB infection LTBI. The current standard regimen is 9 months of Isoniazid 9INH. This regimen has excellent efficacy if taken regularly, but its effectiveness is substantially reduced by poor compliance. Serious side effects, such as hepato-toxicity can occur. Three shorter alternatives have been recommended: 6 months INH 6INH, 2 months Rifampin - Pyrazinamide 2RIF-PZA and 4 months Rifampin 4RIF. Based on some evidence in treatment of LTBI, and extrapolating from extensive experience with treatment of active TB, it is believed that 4RIF has similar efficacy as 9INH. 