Novas ferramentas para o diagnóstico de infecção latente por Mycobacterium tuberculosis

Abstract

This thesis aimed to identify screening strategies for tuberculosis infection (TBI) in healthcare workers (HCW) that enable the most efficient use of available resources. Investigation of TBI in HCWs is recommended in Brazil as part of the worker's pre-employment and periodic (annual) health visits. HCWs with a first tuberculin skin test (TST) induration < 10 mm are invited to repeat the test in one to three weeks to assess the booster effect (induration size increment of 10 mm). Those with a persistent TST < 10 mm will undergo a one-step TST every 12 months. TPT is recommended when conversion (10 mm increment over latest induration size) occurs. We developed, in the first manuscript, a predictive model to identify HCWs best targeted for TBI screening. We carried out a secondary analysis of previously published results of 708 HCWs working in primary care services in five Brazilian State capitals who underwent two TBI tests: tuberculin skin test and Quantiferon®-TB Gold in-tube. We used a classification and regression tree (CART) model to predict HCWs with negative results for both tests. The performance of the model was evaluated using the receiver operating characteristics (ROC) curve and the area under the curve (AUC), cross-validated using the same dataset. Among the 708 HCWs, 247 (34.9%) had negative results for both tests. CART allowed us to identify that physicians or a community health agents were twice more likely to be uninfected (probability = 0.60) than registered or aid nurse (probability = 0.28) when working less than 5.5 years in the primary care setting. In cross validation, the predictive accuracy was 68% [95% confidence interval (95%CI): 65 – 71], AUC was 62% (95%CI 58 – 66), specificity was 78% (95%CI 74 – 81), and sensitivity was 44% (95%CI 38 – 50). Despite the low predictive power of this model, CART allowed to identify subgroups with higher probability of having both tests negative. In the second manuscript, we analyzed the cost-effectiveness of two TB antigen-based skin tests (TBST) using the recombinant ESAT-6 and CFP-10 immunogens (Diaskintest® and C-TST®) and of QFT-Plus® for TBI diagnosis compared with the current standard of care, TST, among HCWs in Brazil. A state-transition Markov model was created, simulating a cohort of 100,000 HCWs (five annual cycles) for TBI treatment scenarios with 3 months of weekly doses of rifapentine (900 mg) and isoniazid (900 mg) (3HP). We adopted the Brazilian public health system perspective. Effects [tuberculosis disease (TBD) averted) and costs for screening and treating TBI were discounted at 5%. Incremental cost-effectiveness per TBD averted was calculated. Hypothetical cohort of 100,000 HCWs of both sexes with a negative result of TST in the previous year. Diaskintest®, C-TST® and QFT-Plus® tests have higher specificity (0.98, 0.98 and 0.97, respectively). Costs with QFT-Plus® were higher due to equipment, human labor and cost of the kit by test. Diaskintest® was the most cost-effective test (US$ 7,042, US$ 5,781, and US$18,892 per case of TBD averted for the 3HP, 6H, and 9H treatment regimens, respectively), including sensitivity analyses. In the Brazilian scenario, Diaskintest® is the most cost-effective test for sequential testing of HCWs.