Tick-Borne Disease in Minnesota: Peridomestic Vs. Non-Home Exposures

BACKGROUND: Tick-borne diseases are an issue of increasing public awareness and public health importance. This is especially true for diseases transmitted by the blacklegged tick (Ixodes scapularis), as incidences are increasing in traditionally endemic areas and cases and exposures are being documented in new areas. In the eastern United States, research has suggested that the majority of human exposures to ticks occur peridomestically, at or near patients’ primary residences, rather than at sites away from home. In contrast, in the Upper Midwest, most exposures are thought to occur at sites away from home rather than in peridomestic settings. 

METHODS: In Minnesota, case patients meeting the CSTE case definition for confirmed Lyme disease, or the confirmed and probable case definitions for anaplasmosis and babesiosis were interviewed to determine potential locations of exposure to ticks. Data from 2011-2014 was analyzed to determine whether reported exposures occurred more frequently at home or at sites away from home. Patients were assigned categories based upon county of residence at time of illness onset to determine whether differences existed for residents of different regions of the state.  

RESULTS: Exposure information was available for 4,892 of 7,020 (70%) of cases from 2011-2014. For all cases, 29% reported only peridomestic exposures, 36% reported only exposures away from home, and 35% reported both. When comparing residents of Minnesota’s five highest incidence counties to the rest of the state, those patients had 3.6 times higher odds (95% CI, 3.0 to 4.3) of being exposed peridomestically rather than away from home. In contrast, residents of the Minneapolis/St. Paul area had 3.5 times higher odds (95% CI, 3.1 to 4.0) than residents of outstate Minnesota of being exposed to ticks away from home.

CONCLUSIONS: Understanding where exposures occur is an important part of accurately assessing risk for tick-borne disease. This is especially true in places like Minnesota, where risk varies considerably across the state. Exposure to ticks in Minnesota clearly occurs both peridomestically and away from home, but rather than being consistent across all cases, the relative importance of peridomestic exposures varies depending on whether patients live in high population or high incidence parts of Minnesota. Additional studies are needed to further describe these differences.