Long-term protective effect of tuberculosis preventive treatment in a region of moderate/high incidence

Preventive treatment of tuberculosis represents one of the main strategies to contain the spread of this disease on a global scale. However, there are different treatment recommendations depending on the target populations and incidence rates in the regions. The sustained effectiveness of preventive tuberculosis treatment in populations living with HIV is a more debated topic, while its application in other highrisk groups, such as close contacts of people with pulmonary tuberculosis, is still little explored. The objective of this study was to analyze the duration of the long-term protective effect of preventive treatment in a region with a moderate/high incidence of tuberculosis. The sample used in this study was based on two multicenter randomized clinical trials that investigated therapeutic regimens of nine months of isoniazid and four months of rifampicin, essentially in contacts of people with pulmonary tuberculosis. Recruitment took place in the city of Rio de Janeiro, characterized by a moderate/high incidence of tuberculosis (93/100,000 inhabitants, or 0.93/1000 per 1000 people per year - ppa). The Notifiable Diseases Information System (Sinan) was consulted to identify Brazilian participants who developed tuberculosis (pulmonary or extrapulmonary) after randomization for a period of up to 12 years. The incidence rates per 1000 ppa of tuberculosis were calculated among those who did not complete and those who completed preventive treatment, and also the rates corresponding to the regimens, stratified by periods: the first 28 months, after 28 months and full period (from zero to 143 months). The failure function, that is, the accumulated probability of failure, was used to calculate the risk ratio (Hazard Ratio – HR) of the occurrence of tuberculosis cases over time considering the scenarios of completeness of treatment and regimens. The log-rank test was used to check whether there was a statistical difference between the curves. The tuberculosis incidence rate result was higher in the first 28 months among those who did not complete the TPT [6.69/1000 ppa [95% Confidence Interval (CI): 2.17; 15.62)] compared to the period after 28 months [1.74/1000 ppa (95% CI: 0.47; 4.45)]. There were 16 cases of tuberculosis, half of which occurred within the first 28 months after randomization. There was greater protection due to complete treatment (log-rank test p=0.042) in this period when compared to incomplete treatment. These results suggest that there is no increased risk of tuberculosis up to 12 years after a course of TPT in contacts living in an area of moderate∕ high incidence of tuberculosis, and that therefore, in this setting, there is no evidence that there is a need for retreatment. with TPT.