This study investigated factors associated with leprosy-related disability in a large Brazilian set of cases. Among 16,376 new cases of leprosy analysed, were less likely to present grade 1 or grade 2 physical disabilities women, those living in the North, Northeast and Center-West regions or in high incidence clusters, in urban areas and with greater household crowding. In contrast, being over 15 years of age, with a lower level of schooling, not working and being multibacillary increased the chances of presenting grade 1 or grade 2 physical disabilities.
The higher likelihood of leprosy-related disabilities found among those older than 15 years is similar to previous studies. In a hyperendemic area of the Center-West region of Brazil, the estimated risk ratio of grade 2 disability was 5.3 times higher among patients aged ≥ 45 years . In the state of Minas Gerais, a retrospective study showed that age above 15 years was an important risk factor for the development of physical disability in leprosy patients . A study of patients residents in the state of Maranhão showed a progressive increase in the chances of developing physical disability among those older than 15 years, ranging from 3 to 10.4 times more . Considering the duration of the disease is directly related to age and, given the chronic profile of leprosy effects, increasing age may result in more advanced disabilities [17, 19].
Regarding gender, some studies did not identify an association between gender and the level of disability [20–22]. However, as in this study that used data from all over Brazil, other studies report higher grades of physical disability among male individuals with leprosy [17, 23].
Men are generally more exposed to M. leprae and have reduced contact with health care, which may delay diagnosis and increases the risk of developing physical disabilities . Data from the Ministry of Health for the general population show that between 2012 and 2016 the detection rate of new cases with physical disability grade 2 was much higher in males with 15.2 cases per 1 million men, while the rate in women was 6.1 cases per 1 million women . Cultural factors may explain the difference between the studies because women may be more likely to seek health assistance than men , while men go when the disease is in a more advanced stage.
Our study also suggests that higher levels of education were negatively associated with the presence of physical disabilities at diagnosis, which is consistent with the literature [16, 17]. Higher education may be associated with a better understanding of the disease and, consequently, better access and utilization of health services. Regular treatment and evaluation, as well as self-care, are aspects that prevent the worsening of leprosy cases [17, 25].
The fact that cases from the Northeast and the North regions were less likely to present G1D and G2D contrasts the findings from Freitas and colleagues (2016) , which showed greater proportions of G2D in municipalities with higher incidence rates of leprosy. They hypothesize that “in these municipalities, at least in the short term, a consequence of increased surveillance actions may be the initial increase in the ‘detected’ cases of the disease. In turn, this increase may lead to increased tracing of people who have had contact with it and greater detection of cases with grade 2 disability, which previously were not identified. This hypothesis may explain the finding that municipalities with a greater proportion of cases presenting with grade 2 disability also had higher average leprosy incidence rates”. However, the areas with higher endemicity do not have a better structure surveillance and care system, as they are systematically poorer. The clusters are located in areas that are more vulnerable.
Therefore, we hypothesize that this fact is likely due to a more sensitive health staff and surveillance system to case detection, therefore more capable of detecting leprosy cases earlier. Assuming that disability is a marker for late diagnosis, it is expected that regions of high endemicity will show a lower chance of patients presenting with grades 1 and 2 disability. G2D, as already mentioned may indicate a late diagnosis and a suboptimal surveillance system. According to Penna et al. (2009) , access to primary health care units has improved mainly in rural areas and small towns, improving the diagnosis of leprosy in the first decade of this century. However, as her work emphasizes, “the diagnosis of skin diseases depends on the cultural importance given to skin lesions, as well as health-seeking habits among the population.”
The study by Freitas et al. (2016)  looked at risk factors, estimated rate ratios (RR), and identified a high NCDR in the Midwest and North regions compared to the South, large cities and greater urbanization, median and high illiteracy rate, income inequality (Gini index), domiciles’ agglomeration, worse sanitation condition, and percentage of cases with grade 2-disability.
Although we found similar evidence that individuals living in urban areas were at a greater risk of leprosy detection than individuals living in rural areas, we did not find evidence of an association of household density with leprosy risk in the full cohort. It is, however, noteworthy that in subgroup analyses increased household density (more than one resident per two rooms) was associated with an increased leprosy risk in children, a group indicative of active transmission .
The association between the proportion of multibacillary leprosy and presentation of G2D has been shown in the past [16, 26, 27]. Studies conducted in some Brazilian cities indicate that at the time of diagnosis, the educational level variables and operational classification are statistically associated with the development of physical disabilities (p < 0.05). It is emphasized that multibacillary individuals are twice as likely to develop sequelae as paucibacillary individuals .
Our study has several strengths: the large sample size and extensive follow up period allowed us to evaluate determinants of disability to the extent that is rarely possible. This study linked data from over 100 million individuals and was able to assess factors associated with physical disability in an unprecedented way, also as we were able to evaluate a wider range of variables present in CadÚnico. Unlike other studies, we analyzed the most vulnerable fraction of the Brazilian population, as this is the profile of individuals enrolled in CadUnico.
Nevertheless, our study has some limitations. The use of secondary data originated from routine surveillance activities always brings the issue of completeness of information. We did not have complete information on disability evaluation at diagnosis (n = 1,557) and at discharge. The latter was poorly collected to an extent that does not permit to analyze. Efforts should be undertaken to stress the importance of performing this evaluation at discharge and record it in the information systems. Other factors associated with disability were not available in our database and therefore, could not be assessed, such as health services characteristics and patients’ perception and knowledge about leprosy.