Influence of precipitation accumulation and extremes on leptospirosis cases in Colombia

<p>Environmental variables like temperature and precipitation pose a direct influence on waterborne and vector-borne diseases like leptospirosis, malaria, dengue, among others (Kifle, M. M., et. al, 2019; Andre-Fontaine, G., Aviat, F., &amp; Thorin, C., 2015; Mantilla, G., Oliveros, H., &amp; Barnston, A. G., 2009). Therefore, the climatic forcing over those variables is key to understand the contagion dynamics. Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira that affects humans, domestic animals, and wildlife. In Colombia, 85% of leptospirosis cases are concentrated in 10 of its 32 departments (Arias-Monsalve, Salas-Botero, &amp; Donalisio, 2021). Methods: Annual cycle of leptospirosis cases at national and departmental level were computed and compared with changes in number of cases occurred during the different phases of El Ni&ntilde;o Southern Oscillation-ENSO (Neutral, El Ni&ntilde;o and La Ni&ntilde;a (Arias-Monsalve &amp; Builes, 2019). Additionally, for municipalities with the highest number of cases, the leptospirosis Relative Risk based on the incidences computed for the days exceeding thresholds of accumulated rainfall at 7, 14, and 21 lags was estimated. Results: Regarding the influence of extreme rainfall events as the ones presented during El Ni&ntilde;o and La Ni&ntilde;a phases of ENSO, we found that at the national level, the monthly number of cases raised a 25% during La Ni&ntilde;a and decreased by 17% during El Ni&ntilde;o. At the departmental level, we detected an increase of cases in both phases of ENSO, depending on the location in the country. With respect to the accumulation of rainfall that occurs during the different seasons in the country, we found a statistically significant association between excess rainfall and leptospirosis relative risk higher than 1 at different lags for cities in the Orinoco, Caribbean, Pacific, and Andes regions. Conclusions: In Colombia, there is a relationship between leptospirosis and accumulated rainfall as well as with the excess and lack of rainfall related to ENSO. The contrasting results from each spatial and temporal scale, reinforce that leptospirosis is a multidimensional disease with high complex interactions among its determinants.</p>