Leprosy is a chronic infectious-contagious disease caused by Mycobacterium Leprae, an obligate intracellular bacillus that affects the skin and the peripheral nervous system [1]. Leprosy is characterized as a slowly advancing disease and, due to the characteristics of the bacillus, presents high infectiousness and low pathogenicity [1], being a potentially disabling and stigmatizing disease. For diagnosis and definition of the treatment regime with polychemotherapy (PCT), two operational classifications are used that are based on the number of cutaneous lesions, according to the following criterion: Paucibacillary Cases (PB) with up to five skin lesions; Multibacillary Cases (MB) with more than five skin lesions [2].

The disease is part of the group of neglected diseases and is relevant for public health due to its magnitude and range, causing disabilities in low-income and economically active populations [3]. Among the infectious diseases, it causes the greatest number of permanent disabilities.

The high burden of the disease signals the maintenance of the epidemiological chain of transmission, representing one of the most important epidemiological indicators [3]. Although approximately 30 years have passed since the introduction of multidrug therapy (dapsone, rifampicin and clofazimine), prevalence and incidence rates remain considerable in the country. This demonstrates that other factors play a decisive role in its causal network, such as the biology of the etiological agent, the genetic or immunological characteristics of the host, and social and economic factors, such as precarious living conditions, migration, malnutrition and poverty, among others [4,5]_.

In 2014, 31,000 cases were reported in Brazil, with a detection rate of 15.31 cases per 100,000 inhabitants and a prevalence rate of 1.56 cases per 10,000 inhabitants, putting the country second in the global ranking, only behind India [6]. Also in 2014, Brazil presented a detection rate of cases with grade 2 disability of one case per 100,000 inhabitants [7].

It should be highlighted that Brazil is the only country in the Americas that has been unable to eliminate leprosy (prevalence < 1 case per 10,000 inhabitants).

Since 2000, a movement has been ongoing in Brazil to reduce the burden of leprosy through strategies that are intended to expand the actions to the entire Health Care Network. These include early diagnosis and qualification of patient care, promoting the decentralizion of diagnosis, treatment and prevention actions to Primary Health Care (PHC), the reorganization of services, disclosure regarding the characteristics, signs and symptoms of the disease and universal access [8].

Another strong point is the identification of the most problematic areas of the disease which, once identified, can be the target or focus of healthcare or intersectorial actions, considering the relationship with social determinants [5].

In a literature review that used the descriptors ‘spatial analysis’ AND ‘leprosy’, a large number of articles related to the theme were retrieved, considering different branches or approaches to the clinical aspects of the disease [9], the evolution of the treatment (cure or abandonment) [10], disabilities and late diagnosis [11]. In general, the majority of studies aimed to provide a more exploratory description of leprosy in space, without considering the risk certain communities are exposed to in relation to others. Depending on the risk, emergency measures need to be adopted immediately to solve it or avoid the dissemination of the disease. Inferences regarding risk are an important tool for management, because they permit targets to be outlined and priority levels to be defined. Risk is traditionally focused on the quantification of the probability of negative consequences of one or more factors identified as harmful to health [12].

In view of the importance of advancing health policies in Brazil to eliminate leprosy and provide more solid research approaches to measure the risk or vulnerability in some communities, the aims established were to outline a case profile according to the operational classification of the disease and to identify areas of greater and lesser risk for the occurrence of leprosy.

The aim of the study was to outline the case profile according to the operational classification of leprosy and to identify areas of greater and lesser risk for the occurrence of the disease. A statistically significant association was observed for the gender variable, with a higher occurrence of MB forms among men; among the MB forms, more disabilities were also identified at the moments of diagnosis and cure.

Regarding age, it was observed that the subjects most affected by the MB form were between the ages of 15 and 59 years, a phenomenon that has been observed in other contexts in Brazil [23]. This age range refers to the economically active age ranges of the population, in which the health services should concentrate on preventive measures, with the diagnosis, treatment and identification of the appearance and development of lesions, disabilities and reactive conditions. Early intervention avoids or minimizes the high social cost the disease provokes, due to the withdrawal of this population from productive activities.

The significant predominance of male cases in the MB form can be related to the physiopathological mechanisms of the disease. However, this aspect has not been explored nor well clarified in the scientific literature. Other studies have shown that males are more vulnerable, presenting more severe and disabling clinical forms, at the moment of the diagnosis as well as at the time of completing the medication regime [24–26].

Considering females, in the last two decades, there has been a decline in the number of women with the more severe clinical forms, which strengthens the hypothesis raised. However, the literature shows that women tend to visit health services earlier and attend more regularly [27], which should also be considered in the causal line of the disease.

Concerning the educational level of the subjects, despite the lack of a statistically significant association, the highest proportions of MB cases presented elementary education, in accordance with findings of other studies [28]. A case-control study by Kerr-Pontes [28] suggested that low education acts as a risk factor for the transmission of leprosy. In a study conducted in a city in the state of Tocantins—Brazil, it was suggested that low education is associated with the development of physical disabilities [23].

The number of disabilities at the moment of diagnosis and at the end of the treatment among MB cases was also highlighted in the study, as an aspect that should be considered in the planning and organization of the health services.

Studies indicate that MB patients present 5.7 times greater chance of presenting disabilities, mainly at the end of treatment, when compared to PB patients [29]. The result raises the hypothesis that MB cases are diagnosed later, with a higher grade of neural commitment, which can favor the development of disabilities, closely linked to the time factor [30].

The disabilities reflect the late diagnosis and the quality of care delivered in the context of the health services. If the disability staging of the patient evolves, the technologies the health agents use are, most probably, not suitable or in accordance with the needs of the patient.

In Brazil [2], it is recommended that the health services, especially Primary Health Care, assess and determine the grade of disability of the leprosy patient at the moment of diagnosis, at least once per year during the treatment and at the end of treatment, identifying and preventing physical deformities as early as possible.

The grade of physical disability can be attributed not only to late diagnosis, but also to neuropathies, to treatment irregularities, mainly related to the administration of MDT, and to self-care advice, such as the use of eyewashes, moisturizers, maintenance of domestic appliances and clothing [23].

The present study also evidenced the predominance of the dimorphic and lepromatous clinical forms, a phenomenon also demonstrated in other research scenarios [31–35]. The transmissible clinical forms, dimorphic and lepromatous, due to their high bacillary load, can be highly disabling and stigmatizing, being the main reservoir of the disease [2,8]. Hence, the large proportion of new cases of these clinical forms indicates errors in the active detection of cases and in the search for communicants [31,36].

Through the scanning statistics, risk areas can be stratified and census sectors identified that are inclined toward the establishment of statistically significant clusters for leprosy, in space as well as in space-time. This method permits the spatial distribution of cases to be understood, testing whether the pattern observed is random, regularly distributed or clustered. It also permits the existence of possible environmental factors and the extent of the infection risk to be identified [37].

The high-risk clusters, in the spatial as well as the spatial-temporal analysis, included the West, North and Central Health Districts, which comparatively showed great similarities in the socioeconomic profile and in the occupation profile of their populations. The North Health District had the lowest social indicators among the five health districts studied, with the highest percentage of people earning less than one minimum wage, the lowest Gross School Attendance Rate (TBFE), the lowest Municipal Human Development Index in Education (MHDI-E) and the largest number of subnormal clusters (communities) in the city [38].

In the West District, the health network was more complex, having the largest number of SUS health services, with the second highest percentage of exclusive users. A high percentage of residential housing was identified, with a considerable number of residents per household and a predominance of households with incomes between one and five minimum wages. The Central Health District, in turn, consisted of the oldest neighborhoods of the city, with a traditional service network, without coverage of the Family Health Strategy (FHS), with the main referral center for the treatment of leprosy cases situated there [38]. The district presented a significant percentage of people over 60 years of age and a high burden of chronic health conditions among its inhabitants.

Concerning the low-risk areas identified in the study, it was noticed that the East and South Health Districts corresponded to the protection areas in the spatial and spatial-temporal analyses. The East and South Districts were both characterized by good TBFE and MHDI-E rates and a low rate of population without income. It should be highlighted that the East District possessed the highest percentage of families earning 50 or more minimum wages and the lowest percentage of exclusive SUS users.

The low-risk areas in the city should be highlighted and analyzed with caution in terms of the spatial behavior of leprosy, as the representation of these clusters can evidence errors in the detection of causes by the health services in the “protection” areas for leprosy. This can result in underreporting and/or late diagnosis, serving as an alert for the need to intensify active search actions in order to detect a larger number of cases earlier in these regions [39].

The risk clusters estimated by the scanning statistic revealed the focal and unequal behavior of leprosy among the regions of the city, showing that neighborhoods in the North, West and Central Districts presented populations at high risk of catching the disease. The relationship between the disease and these regions can be associated with the fact that they include the neighborhoods with the greatest social inequalities [35,38,40], with precarious housing, many residents per household, low income and low education, which are factors that favor the dissemination of leprosy [37].

In this context, studies demonstrate that populations exposed to social vulnerabilities, such as unhealthy housing conditions, basic sanitation deficits, low per capita income, irregular occupation of places unsuitable for habitation and many people sharing the same house, represent the main factors for leprosy [18,31,34,36,41,42,43], which, in terms of spatial distribution, presents the focal behavior the disease, as evidenced in earlier studies [1,35,44,45,46,47,48].

It should be highlighted that places with many people living in the same house are the main source of maintenance of the leprosy transmission chain and form the domestic contacts. People living near individuals with leprosy and their social contacts have a greater risk of infection [49]. Frequent clusters are not only associated with lower socioeconomic levels and populational clusters, but are also related to shortages in health services [31].

Concerning the constitution of the care network for leprosy patients, the city follows a centralized and verticalized model, in which municipal referral centers serve as the main access for the entry and follow-up of cases. The municipal care flowchart recommends that, when primary health care services identify a suspected case of the disease, they should forward it to the municipal referral centers to confirm the diagnostic hypothesis and monitoring of the case.

Although the current strategies for the control and elimination of the disease have provided positive results, mainly in the last three decades, they are still considered insufficient to eliminate the disease. The condition identified as essential to achieve the target of elimination of the disease, as proposed by the WHO, is the increased supply of health services through the decentralization of control actions in the cities and the inclusion of leprosy treatment in the Primary Health Care services, mainly in areas of social inequality [9].

The strengthening of PHC, with improved access to the health services, the earlier and more effective detection of leprosy cases, the active search for communicants by Community Health Agents’ (ACS) and the free distribution of MDT are essential strategic actions to eliminate the disease [45]. However, other measures attributed to PHC should be highlighted. The community’s understanding of leprosy (its transmission mechanisms, clinical manifestations and treatment) should be widely discussed and valued, in order to empower the population and reduce the stigma the disease causes, which is still one of the main factors that impede the elimination of leprosy [50]. The advance towards the elimination of leprosy should be based on contact surveillance, on the prevention of multidrug resistance, on the prevention and rehabilitation of physical disabilities and on the reduction of the stigma associated with the disease [5].

The results of this study suggest that the distribution of leprosy is restricted to spaces where a number of factors coincide for its production, including environmental, individual, socioeconomic and health service organization factors.

In the last two decades, spatial analysis has been frequently used as a leprosy control tool in Brazil and in countries with a high prevalence of the disease [44,51]. According to the WHO, this is an effective management tool for disease elimination programs, with its use being recommended in all endemic countries [52]. The identification of spatial clusters through an ecological study is a strategic tool to enhance the understanding about the distribution of a disease and a health resource allocation tool [37]. Being a neglected endemic disease and a severe public health problem, knowledge about the spatial distribution of leprosy and identification of risk areas for the disease are fundamental for its control, being important measures to improve the surveillance actions in certain locations [45].

This study only considered the secondary data available, therefore there might have been underreporting of cases in the areas with lower spatial risk.

These findings contribute to the identification of risk areas for leprosy, presenting elements to consider in the organization and strengthening of the health services in these places in terms of the active search for cases. Considering the early diagnosis and the empowerment of this population, awareness about leprosy needs to be increased and people encouraged to work in partnership with the health services to deal with the problem. Furthermore, social institutions within these areas, such as churches, kindergartens and schools, should be mobilized to work jointly with the health services, as they are located in risk areas.

The study permits a reflection about the health services in these clusters and the mechanisms or technologies these services use to provide access for leprosy patients. Due to the number of grade 2 disabilities found, advances are needed, not only in early diagnosis, but also in the management of cases throughout the treatment, preventing patients from becoming worse after the diagnosis. Therefore, another possibility is the introduction of self-care workshops, preparing patients and families to cope with the disease, with the taboos, prejudices and stigma, and demonstrating how to avoid disabling accidents in the home and work environments, permitting their physical and social rehabilitation. In view of the above, the study contributes to the advance of knowledge in this area and to advances towards the eradication of leprosy in Brazil.