TO THE EDITOR:

In the article by Rabahi et al.(1) published in volume 43, issue 6, of the JBP in 2017, the authors concluded that "The changes in tuberculosis treatment [fixed-dose combination implemented by the Brazilian Ministry of Health] were unable to contain the decrease in cure rates, the increase in treatment abandonment rates, and the increase in [multidrug-resistant tuberculosis] MDR-TB rates, being associated with increased mortality from pulmonary tuberculosis during the study period." Considering that this statement published in the major means of scientific dissemination of the Brazilian Thoracic Association may have a major impact not only on the Brazilian medical community but also on the health professionals engaged in the fight against tuberculosis, we would like this letter to be likewise published in the JBP. Some comments must be made about methodological issues that certainly influenced the conclusions of the aforementioned study.(1)

It is known that evaluation of the level of scientific evidence should be a routine activity of health professionals, but various barriers prevent this from happening. Studies on the impact of public health program interventions require the application of specific methods that consider both the use of an appropriate study design and well-constructed theoretical causal models. Since the discovery of Mycobacterium tuberculosis as the causal agent of tuberculosis, various models of disease determination have been proposed.(2) Initially, these models were uni-causal, based only on this etiologic agent. However, successive failures to control tuberculosis have led to the recognition of a broad range of potential disease determinants, and the uni-causal models have been replaced by complex models, which, in addition to the aspects related to the agent, include determinants ranging from those related to the person with tuberculosis to those related to the social and programmatic context that surrounds him or her.(2) Complex causal models have also been proposed to study interventions. Therefore, attributing solely to a new treatment the outcomes of an intervention, that is, stating a single cause relationship, is an important conceptual limitation since it disregards the multi-causal complexity at play, especially if observational studies are proposed instead of studies with experimental designs, such as randomized clinical trials or even cluster randomized trials.

Conversely, the use of interrupted time series analysis techniques requires meeting some conditions, the most important of which being that the only change affecting the outcome measure in the period is the intervention of interest.(3,4) An article by Linden,(5) which was used by Rabahi et al.(1) as a reference for performing interrupted time series analysis, also reinforces that caution is needed in drawing inferences when potential confounding factors, such as concomitant policies and programs, vary during the study period. It is known that, during the period studied by Rabahi et al.,(1) other important changes occurred that could affect treatment outcomes, such as the lack of nationwide use of tuberculin testing within the health care system; the improvement in diagnosis, with the implementation of the Xpert MTB/RIF assay(6); and the economic crisis that unequally affected the population at highest risk for unfavorable treatment outcomes because of their social vulnerability.

In addition to the limitation that potential confounding factors were disregarded, there is the fact that the treatment was not implemented uniformly in Brazil, with implementation occurring early in some states and later in others. In the study by Rabahi et al.,(1) the intervention time frame chosen does not seem appropriate, given that the study that validated the implementation of the supervised treatment in the health care system was completed only in September 2010, in five cities surveyed.(7) Therefore, during data analysis, line fitting should consider heterogeneity in the treatment's adoption and use (whether treatment was supervised or not) and Family Health Program coverage by city, as well as socioeconomic variables.(8)

The inferences drawn by the authors must also be considered, since not detecting a relationship between an exposure and an outcome should not be interpreted as "there is no relationship between them." The study by Rabahi et al.(1) could not detect the impact of the new treatment on cure and treatment abandonment rates, and it is not correct to state that "the changes in tuberculosis treatment were unable to contain the decrease in cure rates, the increase in treatment abandonment rates, (. . .)" because the inability to verify this relationship may be due to the low statistical power of the study. Additionally, some results were presented in a format that is difficult to interpret, such as in Figure 2,(1) given that there are confidence intervals that include null values but show p values less than 0.05 (Figures 2C and 2G). Furthermore, Figure 2G presents a line with a positive slope and a negative estimate for the parameter.

Therefore, we consider that important methodological limitations and misinterpretation of results have led to conclusions with a low level of scientific evidence, and disseminating this knowledge without criticism is inconsistent with good practices of collective health and health research.
REFERENCES

1. Rabahi MF, da Silva Júnior JLRD, Conde MB. Evaluation of the impact that the changes in tuberculosis treatment implemented in Brazil in 2009 have had on disease control in the country. J Bras Pneumol. 2017;43(6):437-444. https://doi.org/10.1590/s1806-37562017000000004
2. Maciel EL, Reis-Santos B. Determinants of tuberculosis in Brazil: from conceptual framework to practical application. Rev Panam Salud Publica. 2015;38(1):28-34.
3. Penfold RB, Zhang F. Use of interrupted time series analysis in evaluating health care quality improvements. Acad Pediatr. 2013;13(6 Suppl):S38-44. https://doi.org/10.1016/j.acap.2013.08.002
4. Bernal JL, Cummins S, Gasparrini A. Interrupted time series regression for the evaluation of public health interventions: a tutorial. Int J Epidemiol. 2017;46(1):348-355. https://doi.org/10.1093/ije/dyw098
5. Linden A. Conducting interrupted time-series analysis for single-and multiple-group comparisons. Stata J. 2015;15(2):480-500.
6. Durovni B, Saraceni V, van den Hof S, Trajman A, Cordeiro-Santos M, Cavalcante S, et al. Impact of replacing smear microscopy with Xpert MTB/RIF for diagnosing tuberculosis in Brazil: A stepped-wedge cluster-randomized trial. PLoS Med. 2014;11(12):e1001766. https://doi.org/10.1371/journal.pmed.1001766
7. Braga JU, Trajman A. Effectiveness of RHZE-FDC (fixed-dose combination) compared to RH-FDC + Z for tuberculosis treatment in Brazil: a cohort study. BMC Infect Dis. 2015;15:81. https://doi.org/10.1186/s12879-015-0820-4
8. O Brasil pode alcançar os novos objetivos globais da OMS para o controle da TB? Rev Epidemiol Servico Saude. [Epub ahead of print]