n Medical Technology SA - The effect of isoniazid preventive therapy on the occurrence of tuberculosis in Lesotho, Southern Africa - research

Volume 32 Number 2
  • ISSN : 1011-5528


Lesotho faces a catastrophic syndemic of HIV and tuberculosis (TB). In 2011, the government of Lesotho launched isoniazid preventive therapy (IPT) as a once-off intervention to reduce the occurrence of TB in HIV-positive people. This study evaluated the effectiveness of IPT and the durability of its effectiveness based on Cox’s proportional hazards regression analysis of 2 955 records randomly sampled from six districts of Lesotho. The overall TB incidence rate was 2.0 per 100 person-years in 12 208 person-years. Thirty-nine (15.9%, n=246) patients developed TB after IPT. TB incidences per 100 person-years by timing of IPT were as follows: (a) IPT before ART (1.7); (b) IPT after ART (1.8); (c) no IPT (2.6); (d) IPT within one year of ART commencement (1.3) and (e) IPT 3-5 years after ART initiation (2.3). Gender, baseline World Health Organisation (WHO) clinical staging, district category and time to IPT relative to ART commencement emerged as significant predictors of TB occurrence. Increasing time to IPT by one six-month interval increased the risk of contracting TB by between 6% and 59. Further, IPT effectiveness rapidly deteriorated after four years. This indicates that delayed IPT after ART commencement significantly affects the effectiveness of this intervention. The need to consider booster doses of IPT cannot be overemphasised.

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