[Epidemiology of leptospirosis in the wetlands of Southern Spain].

OBJECTIVE: To find out whether the leptospirosis incidence rate among red swamp crayfish collectors in the harvesting season is higher than in the general population, and to identify risk factors and assess the direct and indirect health costs associated with leptospirosis seroconversion.

METHOD: This study was carried out between 1 July 2017 and 31 March 2018 in the municipality of Isla Mayor (Seville, Spain). It took the form of a prospective cohort study (exposed population: swamp crayfish collectors; non-exposed population: general population). The population was invited to take part in a prevalence study to be conducted using the ELISA qualitative technique, and informed consent was obtained from those who agreed. Negative serology cases were then included in the cohort study. Both cohorts were monitored clinically and symptomatic cases were serology tested. A second serum sample was taken from the swamp crayfish collectors at the end of the monitoring period to detect asymptomatic cases. Serovars were confirmed by microscopic agglutination testing. A bivariate descriptive analysis was carried out and cumulative incidence and relative risk were calculated, with positive serology being taken as the dependent variable.

RESULTS: A total of 278 people were included in the study, of whom 92 made up the swamp crayfish collectors cohort and 186 the general population cohort. Women made up 46.8% of the sample, but only 29.3% of the collectors cohort. The mean age was 45.1 (±16.4) years. Nine cases of seroconversion were detected: eight among swamp crayfish collectors and one in the general population. Overall cumulative incidence was therefore 3.2%: 8.7% in the exposed group and 0.5% in the non-exposed group. Relative risk was 16.2% (95% confidence interval: 2.1-127.4). The total cost of medical assistance and illness-related losses associated with leptospirosis was 1568€/case.

CONCLUSIONS: Leptospirosis in Isla Mayor is strongly associated with red swamp crayfish collecting. It's incidence here is much higher than that reported in studies published in other countries.