Abstract
Lyme disease is a well-recognized public health problem in the USA, however, other tick-borne diseases also have major public health impacts. Yet, limited research has evaluated changes in the spatial and temporal patterns of non-Lyme tick-borne diseases within endemic regions. Using laboratory data from a large healthcare system in north-central Wisconsin from 2000–2016, we applied a Kulldorf’s scan statistic to analyze spatial, temporal and seasonal clusters of laboratory-positive cases of human granulocytic anaplasmosis (HGA), babesiosis, and ehrlichiosis at the county level. Older males were identified as the subpopulation at greatest risk for non-Lyme tick-borne diseases and we observed a statistically significant spatial and temporal clustering of cases (p < 0.05). HGA risk shifted from west to east over time (2000–2016) with a relative risk (RR) ranging from 3.30 to 11.85, whereas babesiosis risk shifted from south to north and west over time (2004–2016) with an RR ranging from 4.33 to 4.81. Our study highlights the occurrence of non-Lyme tick-borne diseases, and identifies at-risk subpopulations and shifting spatial and temporal heterogeneities in disease risk. Our findings can be used by healthcare providers and public health practitioners to increase public awareness and improve case detection.
Highlights
Tick-borne diseases pose a significant public health challenge to the USA with evidence of increasing occurrence in the last decade
We identified records of patients with laboratory evidence of non-Lyme tick-borne diseases based on Marshfield Clinic Health Care System (MCHS) electronic health records (EHRs) laboratory codes for human granulocytic anaplasmosis (HGA), babesiosis and ehrlichiosis derived from blood smear, serologic, and PCR tests completed between 2000–2016
Given the small sample size of ehrlichiosis cases (n = 30) and to narrow the focus to a common vector for the pathogens under study (I. scapularis), we only considered cases of ehrlichiosis caused by E. muris eauclairensis (n = 15) endemic to Wisconsin and recently described in humans [17,24]
Summary
Tick-borne diseases pose a significant public health challenge to the USA with evidence of increasing occurrence in the last decade. Lyme disease is the major leading cause of tick-borne disease in the USA and has been extensively studied, the three leading causes of tick-borne disease (anaplasmosis/ehrlichiosis, Rocky Mountain spotted fever and babesiosis) accounted for 42,090 cases (37.3%) in 2016–2018 [1]. These diseases have received less attention compared to Lyme disease. Non-Lyme tick-borne diseases are of concern for states in the upper Midwest including Minnesota and Wisconsin, an endemic region for non-Lyme tick-borne diseases with a high incidence of HGA and babesiosis [4]
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