Prevalence of latent tuberculosis and associated factors in patients with chronic kidney disease on hemodialysis

Objective: to identify the prevalence of latent tuberculosis in patients with chronic kidney disease on hemodialysis and associated factors. Method: a cross-sectional study conducted with 176 patients with chronic kidney disease on hemodialysis. The tuberculin test was performed with the standardized antigen, distributed by the Brazilian Ministry of Health, and the reading occurred after 72 to 96 hours of the application. An association test (Chi-square, Fisher’s exact), prevalence ratio, and multivariate regression tests were performed. Results: the prevalence of latent tuberculosis diagnosed through Tuberculosis Skin Test was 8.5% (15/176). The “has/has had diabetes” (aOR: 0.117; 95%CI: 0.015-0.92) and “having regular garbage collection (aOR: 0.076; 95%CI: 0.008-0.702) factors were associated with a lower probability of having a Positive skin test. Conclusion: the low prevalence of latent tuberculosis identified and the factors associated with it reinforce the need for screening for latent tuberculosis infection for diabetics combined with an analysis of previous risk factors and comorbidities.


Introduction
Tuberculosis (TB) is still a severe public health problem worldwide, being among the 10 main causes of death (1) . Official data from the World Health Organization (1)(2) report that nearly 10 million people in the world have fallen ill with TB every year and that more than 1.5 million have died from the disease in 2018.
Ending the global TB pandemic is one of the goals of the Sustainable Development Goals (SDGs), which aim to reduce by 90% the deaths and by 80% the incidence of the disease until 2030, comparing with the 2015 levels (2) . Brazil still records a high prevalence of TB, with 72,000 new cases in 2018, focused mainly on minorities (prisoners, people with HIV/AIDS, homeless population) more vulnerable to the disease (3) .
Patients with some type of immunosuppression, such as those with Chronic Kidney Disease (CKD), are more susceptible to TB infection (4) . In these patients, uremia reduces the expression of the co-stimulatory B7-2 molecule in cells presenting the antigen, which alters the function of the polymorphonuclear cells and interferes in the phagocytic, migration, and chemotactic efficiency, reducing the capacity of cells to kill intracellular microorganisms. In patients with CKD on hemodialysis, the risk of developing TB is 6.5 to 52.5 times higher than in the general population (4)(5) .
These patients present great risk of developing active TB from a previous latent infection (6) and greater risk of reactivating latent TB, or even its atypical presentation. It is because of this that there are explicit recommendations for the investigation of latent TB in patients that are being or will be subjected to immunosuppressive therapies/conditions, including CKD and transplanted individuals (7) .
A considerable gap in the knowledge of the prevalence of latent TB and associated factors in patients with CKD on hemodialysis was observed in the literature in general (7) , mainly in Brazil (3) , which makes it difficult to establish a situation overview and thus setting up public policies.
In Brazil, the TB skin test, also called a Mantoux tuberculin skin test (TST), is a classic diagnostic tool to identify latent TB and is essential for patients with CKD on hemodialysis (8) . Considering that the strategies in

Results
In the sample of 176 patients, the study estimated a prevalence of 8.5% reactors (positive TST).

Discussion
We recorded a low prevalence of latent TB among patients with CKD on hemodialysis (8.5%), when compared to other international and national surveys. A study conducted in Taiwan (9) reported a prevalence of 11%, very close to another study carried out in Brazil (5) , which recorded a prevalence of 11.2% in the same conditions.
Among the predictive factors for latent TB, we highlight the presence of pre-existing comorbidities (diabetes mellitus) and socio-sanitary conditions (garbage collection). showing that the social problems of the population have a direct influence on the onset of the disease (11) .
On the other hand, our data found a protection relation between the presence of CKD and diabetes mellitus; in contrast to the literature, which points out that there is a moderately increased risk of latent infection by TB in patients with diabetes. This disease compromises the immune system and increases the general risk, up to three times, of the infection to evolve into active TB (12)(13) .
However, this same impairment of the immune response must also be one of the responsible elements for the lower response of the individual in the TST (12)(13)(14) .

Conclusion
The prevalence of latent TB among patients with CKDon hemodialysis was not high. Among the predictive factors for latent TB, the presence of pre-existing comorbidity (diabetes) and a socio-sanitary condition (garbage collection) stand out. Therefore, it is necessary to be attentive to the possibility of developing active TB, with a generally extra-pulmonary clinical presentation or spread in these patients, since the diagnosis tests cannot detect all the reactors, and TB is associated with chronic disease and unhealthy environments, contributing to the high rates of morbidity and mortality of this population.
Considering that this is a highly prevalent disease on a world scale, focusing on latent TB among people with chronic diseases, like those with CKD, may increase the diagnosis capacity and lead the creation of algorithms and/or protocol with this purpose.