The correlation between local weather and leptospirosis incidence in Kandy district, Sri Lanka from 2006 to 2015

Abstract

Background: Leptospirosis is an important public health problem in Sri Lanka. Most people become infected by contact with leptospires in soil and in surface water. Survival of leptospires in the environment depends upon the moisture in soil, humidity, temperature and surface water. Leptospires are spread by flood water and waterways. Therefore, the weather of an area influences the leptospirosis incidence of that area. Objectives: To find out the correlations between the leptospirosis incidence in the district of Kandy, Sri Lanka, and local weather variables and then to explore the utility of the findings. Methods: We gathered data on reported leptospirosis cases in the Kandy district and mid-year population data and calculated weekly incidences for 2006 to 2015. Daily weather data from Katugastota weather station was obtained and converted into weekly data. We plotted time series graphs and observed the correlation between six aggregated weather parameters and leptospirosis incidence. Those weather parameters were rainfall, the count of wet days per week, days with rainfall >100 mm per week, minimum temperature, average temperature and average humidity. Then we looked for correlations between leptospirosis incidence and those weather parameters by performing the wavelet analysis. Results: Our wavelet analysis results show peaks of wet days per week, days with rainfall >100 mm per week, minimum temperature, average temperature and average humidity respectively after 2, 3, 13, 20 and 1 week lags were followed by peaks of leptospirosis incidence. Nadirs (troughs) of rainfall after a week were followed by nadirs of leptospirosis incidence. Conclusions: All weather parameters studied are correlated with local leptospirosis incidence and the climate in Kandy is conducive for leptospirosis transmission. Leptospirosis incidence in the Kandy district is high compared to the national and global incidence. Therefore, leptospirosis preventive work in Kandy deserves more attention, especially during months with favorable weather for leptospirosis transmission.

Trend of leptospirosis and its association with meteorological factors in Thrissur district, Kerala

“…10 Similar results have been found out from studies from Srilanka by Ehelopola et al which showed leptospirosis incidence follows the same pattern of temporal changes of average weekly humidity after a lag period. 12 The current study also found a positive correlation between rainfall and number of leptospirosis cases (Figures 6 and 7A). This relationship have also been found out from the study conducted by Matsushita et al in Philippines who found out that the risk of post-rainfall, leptospirosis peaked at a lag of 2 weeks (using 0 cm/week rainfall as the reference) with RRs of 1.30, 1.53, 2.45, 4.61, and 13.77 for light, moderate, heavy, intense and torrential rainfall (at 2, 5, 16, 32 and 63 cm/week), respectively.…”

Effects of seasonal changes in temperature and humidity on incidence of necrotizing soft tissue infections in Halifax, Canada, 2001-2015

“…A previous study has examined bacterial infection and specific weather factors. Ehelopola et al24 observed a direct association between rainfall and humidity and leptospirosis infections in Sri Lanka. As the authors point out, this association is likely attributable to improved survival of leptospires in moist soil.…”

Understanding leptospirosis eco-epidemiology by environmental DNA metabarcoding of irrigation water from two agro-ecological regions of Sri Lanka

“…The diagnosis of the great majority of the reported cases in Sri Lanka is not laboratory confirmed, thus they can be categorized as clinical suspected cases of leptospirosis. Based on this report system, the annual national leptospirosis incidence is 5.4 per 100,000 population [ 51 – 53 ]. Clinical suspected leptospirosis cases have been reported in the sampling areas [ 54 , 55 ].…”