Correlation between mean temperature and incidence of tick-borne diseases among active duty service members in the contiguous U.S., 2000-2023.

Medical encounter data and reportable medical events from the Defense Medical Surveillance System were utilized to establish that from 2000 to 2023 there were 2,869 cases of Lyme disease and 175 cases of Rocky Mountain spotted fever among U.S. active component service members within the contiguous U.S. Coincident with a 5.3% (0.63°C) increase in annual mean temperature over the course of the 24-year surveillance period, annual Lyme disease incidence rates increased 35.5% overall, concurrently peaking with mean temperature in 2012 and 2016. After adjusting for annual mean, minimum and maximum temperatures, annual total precipitation, and regional climate, in addition to adjusting for age group, race and ethnicity, sex, and service, incidence rate ratios of both tick-borne diseases did not significantly change with increases in climatic variables. Adjusted incidence rate ratios of both tick-borne diseases increased with increasing age group. Annual Lyme disease incidence rates peaked concurrently with annual mean temperatures. Incidence rate ratios for Lyme disease were highest in the Southeast compared to the Northeast, while Rocky Mountain spotted fever incidence rate ratios were highest in the South compared to the Southeast. Annual Lyme disease and Rocky Mountain spotted fever incidence rates ratios increased with increasing age group.