Investigating the spatial patterns and climate dependency of Tick-Borne Encephalitis in Sweden

Sammanfattning: The increasing prevalence of Tick-Borne Encephalitis (TBE) in Sweden is a cause of concern to both individuals and the public health service. The disease is spread via bites from the vector Ixodes ricinus and causes long-term neurological damage in 46% of cases. To date, research in this field has focussed on the relationship between climate and TBE incidence and there is little to no available research regarding the spatial distribution of TBE in Sweden. The aim of this study was to determine whether the relationship between TBE and climate factors is statistically significant and to detect spatial patterns of TBE both nationally and in the endemic Stockholm-Mälaren region in eastern Sweden. The data includes annual TBE incidence from 1986 to 2016. Monthly data was not available. Multiple linear regressions were used to determine the dependency of TBE on climate variables (temperature and precipitation). Many of the explored years show a statistically significant relationship between TBE and at least one climate variable, though using data at a finer temporal scale would produce results with more years showing statistical significance. Getis-Ord Gi' and Local Moran’s I were used in order to detect spatial autocorrelation between TBE incidence points in the Stockholm-Mälaren region. Significant clustering (p < 0.1) was detected in the majority of years in the temporal dataset, with high levels of clustering occurring in southern Stockholm County and along the shores of Lake Mälaren. Climate change increases the risk of ticks and, as a result, TBE spreading further north in Sweden. This study recommends further spatial analysis and modelling of the spread of TBE in relation to climate factors. This will in turn allow policy makers within the public health sector to make informed decisions regarding preventative schemes and rehabilitation programmes. However, it requires that the reporting of TBE incidents takes place on a monthly basis.