Aplicação do Xpert® MRB/RIF Ultra pelo método pool como estratégia para o controle da tuberculose nas prisões

Abstract

Introduction: Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis (MTB), and its distribution in the population is linked to socioeconomic factors, with a high incidence in vulnerable subpopulations, such as those deprived of liberty (PDL). The use of Xpert MTB/RIF® Ultra in systematic screening to identify cases of active TB in this population is not widely implemented due to budget constraints, especially in low- and middle-income countries, requiring new approaches to reduce the costs of its application. Aim: To identify new strategies for systematic screening of TB in prisons using the Xpert MTB/RIF® Ultra cartridge using the pooling method. Methods: In this study, 1,280 sputum samples from individuals from three prisons in Mato Grosso do Sul, Brazil, were tested using the Xpert MTB/RIF 4th Generation. Subsequently, these samples were selected to produce pools of 4, 8, 12 and 16 samples, with each pool containing a single different semiquantitative MTB load positive sputum sample (very low, low, medium and high) together with samples negative until reaching the required number to have 4, 8, 12 and 16 sputa. In addition, pools containing 16 negative samples were used as a control. These pools were tested in the Xpert® MTB/RIF Ultra cartridge, and from these results, it was verified which pool had the highest sensitivity as well as the best cost-benefit ratio to be applied in a hypothetical population of 1,000 individuals with prevalence rates of 0, 5%, 1%, 2%, 3%, 4% and 5%. Results: The overall sensitivity of pools containing positive samples was 94% (n = 94/100, 95% CI: 88-98%), and based on these results, the number of tests needed to identify each TB case was calculated. in each strategy. With a lower prevalence rate (0.5%), pools with more specimens (16) resulted in a significant decrease in the number of tests per TB case. The opposite occurred at a higher prevalence rate (5%), where a pool with fewer samples was more effective. From these data, the cost-effectiveness that the application of these strategies would present in this population was calculated. Pools with larger amounts of samples reduced costs by up to 87% at lower prevalences, while pools with smaller amounts of samples fit better at higher prevalences (57%). Conclusion: These data suggest that the size of the pool chosen is strongly related to prevalence. The higher the prevalence, the pool with fewer samples was more effective, unlike a lower prevalence, where the pool with more samples was more efficient, increasing its cost effectiveness to be applied in systematic screening in prisons.