Leptospirosis incidence and associated factors in Chapecó , Santa Catarina , Brazil

Backgrounds and Objectives: The environmental conditions are directly related to the population’s quality of life and health, which justifies the evaluation of factors associated with the occurrence of certain diseases. This study aimed to evaluate the incidence of confirmed cases of leptospirosis and associated factors in Chapecó-SC. Method: This is a cross-sectional descriptive exploratory study with data obtained from the individual reporting and investigation of records of the Notifiable Diseases Information System database, of the Epidemiological Surveillance Department of the Municipal Health Secretariat, related to all confirmed cases of leptospirosis for the period 2010-2015. Results: 24 positive cases were recorded in the period. Of these, 87.5% affected male individuals aged 12-59 years. 8.3% of individuals reported they had contact with floodwater or mud, and in the other cases, the probable contamination occurred in areas with signs of rodents (70.8%) or with the presence of these animals (41.6%), rivers, streams, ponds or dams (37.5%) and livestock breeding facilities (33.3%). The workplace was the main infection source (41.6%). There was no association between the number of leptospirosis cases and rainfall indexes. Conclusion: It stands out that the infections occurred mainly through occupational exposure, which emphasizes the importance of health services in continuing education and leptospirosis prevention campaigns, mainly those aimed at the health of workers exposed to areas of risk.


INTRODUCTION
Leptospirosis is a febrile infectious zoonosis, caused by the Leptospira bacteria, of which microorganism penetration occurs through damaged skin, whole skin immersed for long periods in contaminated water or through mucous membranes, having an average incubation period of 10 days. 1 The main reservoirs are the domestic or wild synanthropic rodents of the species Rattus rattus (Linnaeus, 1758), Mus musculus (Linnaeus, 1758) and Rattus norvegicus (Berkenhout, 1769), carriers of the serovar Icterohaemorrhagiae, one of the most pathogenic to humans. 2 Among the most vulnerable individuals are people working in the areas of cleaning, sewer cleaning, construction, farmers and veterinarians who are exposed to the risk of occupational contamination, since these professions provide direct contact with Leptospira. 3 In Brazil, leptospirosis is considered an endemic disease, with the first records being made between 1910 and 1940 and reports of several urban outbreaks in the 1960s. 4 During the rainy season, floods and poor sanitation constitute the main risk factors for the occurrence of leptospirosis. 5 Leptospirosis can be considered a disease of social and economic importance due to its high incidence in certain areas, high hospital costs and loss of working days, as well as its lethality, which can reach up to 40% of the most severe cases. 2 Its geographical distribution is favored by the environmental conditions found in tropical and subtropical regions, where the high temperatures and periods of the year with high rainfall rates favor the emergence of seasonal epidemic outbreaks. 6 The greatest risk of contamination associated with flooding waters is due to population agglomeration, socioeconomic and sanitation conditions that are observed in metropolitan regions. 7 Currently, there are records of the disease throughout the country, with a higher number of cases in the south and southeast regions. From the beginning of 2010 until December 31, 2015, 25,162 cases of leptospirosis were recorded in the country, of which 8,399 (33.4%) were identified in the southeast region and 7,643 (30.4%) in the southern region. The state of Santa Catarina had 2,790 (11.1%) cases in this period. 7 In this context, we evaluated the incidence of leptospirosis cases and associated factors in the municipality of Chapecó, state of Santa Catarina, occurring in the period from 2010 to 2015.

METHODS
The present investigation is characterized as a descriptive exploratory study, with data obtained from the Notifiable Disease Information System (SINAN), Department of Epidemiological Surveillance of the Health Secretariat of the municipality of Chapecó, related to all confirmed cases of leptospirosis occurring from 2010 to 2015.
The municipality of Chapecó is located in the western region of the state of Santa Catarina (27°05′47″ S, 52°37′05″ W), at approximately 600 km from the capital city of Florianópolis. It has an estimated population of 205,795 inhabitants, with 91.61% located in the urban area. The per capita Gross Domestic Product (GDP) is R$ 24,839.97. 8 The climate of the region is humid subtropical mesothermal superhumid type, with no defined dry season, with frequent frosts and regular distribution of rainfall. 9 Individual notification and investigation forms were used, which are filled out by the municipal epidemiological surveillance service or health unit professionals and comprise the national SINAN database. The history of the confirmed cases according to the main risk situations to which the infected individuals were exposed in the thirty days prior to the first disease symptoms was assessed. The monthly weather data related to the period of 2010 to 2015 (minimum temperature, mean temperature, maximum temperature, relative average humidity and total rainfall), obtained from the National Institute of Meteorology (INMET), were correlated with the monthly frequency of leptospirosis cases. Pearson's correlation test and PAST statistical software were used to perform the analysis. 10 Only correlations that showed statistical significance were maintained and cited (p <0.05).
The association of leptospirosis cases with the months of the year and the correlation with the six evaluated years, according to the disease occurrence in the municipality, was verified using Principal Component Analysis (PCA). The PAST statistical program was used for the analysis. 10

RESULTS
From January 1, 2010 to December 31, 2015, there were 24 positive cases of leptospirosis in the municipality of Chapecó. Of these cases, 83.3% were men aged 12 to 59 years. (Table 1). There were no records of deaths in the period. The year with the highest number of confirmed cases of leptospirosis was 2011  The epidemiological risk to which individuals reported having been exposed in the 30 days prior to the first symptoms, as well as the possible infection environment that was especially characterized in the locations where the presence of rodents was identified, mainly associated to professional activities, are shown in Table 2.     Livestock breeding represents an epidemiological risk and is likely to be the source of contamination at the workplace for the workers in this area, as the infection can occur from contact with diseased or Leptospira carrier animals, such as dairy cattle and swine herds. 12,13 Of the notified cases in Brazil, approximately 28% are related to rural areas, where transmission occurs indirectly, usually associated with the work process of people dealing with grain production. 14 Thus, leptospirosis can be considered a leading zoonosis in human morbidity and mortality, especially in the population working with subsistence farming. 15 However, the Brazilian urban and periurban environments suffer from rodent infestation due to the disorderly process of urbanization, mainly close to brooks and streams. This has been the predominant factor for the incidence of cases of this disease. 16 The identification of rodents in the work environment may be an important predictor of the presence/density of the wild reservoir of Leptospira. The work environment was indicated as predisposing factor for leptospirosis in workers of the environmental sanitation service in the city of Pelotas, state of Rio Grande do Sul, identified by a serum-epidemiological survey in which the prevalence of recorded leptospirosis infection was 10.4%, being among the highest rates recorded in serological surveys carried out in Brazil. 17,18 Likewise, in the municipality of Garanhuns in the state of Pernambuco, the prevalence of anti-Leptospira spp. antibodies in occupational groups was 5.19%. 19 In Chapecó, no association was found between the number of cases of leptospirosis and rainfall indices, and the appearance of the disease does not coincide with periods of increased rainfall and floods. These data coincide with a study carried out between January 1991 and April 1996, which disclosed that the number of requests for leptospirosis testing at the Public Health Central Laboratory of Santa Catarina (LACEN) decreased in 1992 and 1993, when there were no floods, but the rate of positive results was similar to that of years in which flooding occurred, and lethality was higher, since the diagnosis is made and disclosed at a later date or misdiagnosis occurred due to other diseases with similar signs and symptoms. 20 Regarding this fact, it can be observed that the variation in the incidence of leptospirosis is determined not only by the rainfall index, but by a multiplicity of environmental and social factors, such as lack of basic sanitation and disordered urbanization, which requires skilled professionals and fast diagnosis, as well as responding to the demands that cause the infection. 21 It was observed that the incidence of leptospirosis in Chapecó has a defined seasonality. The concentration of cases in the months of December, January and February coincides with the school vacation period, when students and other people living in urban areas visit and go camping in rural areas. These months are also characterized by higher temperatures, a condition that causes people to be more exposed to contamination by not wearing closed shoes during work activities, for instance.
The records of cases in September may be associated with rainfall, which is usually higher during this period, although no correlation was found with any of the It has been demonstrated that the professional environment is relevant to the disease epidemiology, since it may represent an increased risk of contamination. 22 Professional categories associated with agriculture/farming, veterinary professionals, sanitation workers, among other professions, are more susceptible. 22 In Chapecó, Leptospira infections occurred mainly in environments with occupational-related exposure and, principally, in places with signs of the presence of rodents, near rivers, streams or dams, in livestock breeding facilities, vacant lots, crop fields and grain storage sites, garbage and rubble deposit sites.
Contamination cases caused by contact with floodwater or mud were less significant, showing no association with the occurrence of flash floods and floods, not even considering the higher rainfall indices that occurred in the period. Therefore, it is important and necessary to investigate the cases for timely surveillance and effective prevention and control of leptospirosis. 13 Among the prevention actions is the improvement of actions directed at workers' health, together with primary care, in order to detect early risks, establish timely treatment of those affected, and keep surveillance on alert during the periods of greatest exposure. 13 The knowledge of the determinant causes of leptospirosis, as well as the most vulnerable areas and social groups, contributes to more equitable and effective public intervention policies. 23 In this context, knowledge of infection severity, geographical distribution, involved risk factors and circulating strains is important for the establishment of the regional leptospirosis epidemiology and improvement of preventive measures. 24 It is noteworthy that the work of Environmental Surveillance in environmental health education is of utmost importance as an instrument for zoonosis prevention actions. 25 Finally, the identification of work environments and areas vulnerable to the occurrence of leptospirosis in the municipality of Chapecó, characterize a challenge for Environmental Surveillance and health teams working together with other sectors of public and private services, aiming to both monitor the control of the vectors and work with the instrumentalization and training of workers for disease prevention and the promotion of the population's health, as well as the notification and investigation of the cases, thus minimizing the underreporting of the disease, which can be considered a limitation of this study .
The present study demonstrates the importance of health services in continuing education and campaigns to prevent leptospirosis, mainly aimed at the health of workers exposed to areas of risk. It shows relevant information about the seasonality of leptospirosis occurrence in the municipality that can support the planning and implementation of prevention actions. According to this perspective, it is essential to strengthen prophylactic measures aiming to minimize the disease incidence.