Meteorological influences on the seasonality of Lyme disease in the United States

Abstract

Lyme disease (Borrelia burgdorferi infection) is the most common vector-transmitted disease in the United States. The majority of human Lyme disease (LD) cases occur in the summer months, but the timing of the peak occurrence varies geographically and from year to year. We calculated the beginning, peak, end, and duration of the main LD season in 12 highly endemic states from 1992 to 2007 and then examined the association between the timing of these seasonal variables and several meteorological variables. An earlier beginning to the LD season was positively associated with higher cumulative growing degree days through Week 20, lower cumulative precipitation, a lower saturation deficit, and proximity to the Atlantic coast. The timing of the peak and duration of the LD season were also associated with cumulative growing degree days, saturation deficit, and cumulative precipitation, but no meteorological predictors adequately explained the timing of the end of the LD season.

Figure 1.

Weekly Lyme disease cases (A) and cumulative percentage of annual cases (B) for Maryland and Minnesota in 2001. Solid lines in (A) represent actual number of weekly cases for each state and dashed lines represent the smoothed number of cases using a fifth-order polynomial. (C) The second-order finite difference of the weekly case count for each state was used to calculate the beginning and end of the Lyme disease season for each state and year. The dotted lines in (A–C) represent the beginning week for each state.

Figure 1.

Weekly Lyme disease cases (A) and cumulative percentage of annual cases (B) for Maryland and Minnesota in 2001. Solid lines in (A) represent actual number of weekly cases for each state and dashed lines represent the smoothed number of cases using a fifth-order polynomial. (C) The second-order finite difference of the weekly case count for each state was used to calculate the beginning and end of the Lyme disease season for each state and year. The dotted lines in (A–C) represent the beginning week for each state.

Figure 1.

Weekly Lyme disease cases (A) and cumulative percentage of annual cases (B) for Maryland and Minnesota in 2001. Solid lines in (A) represent actual number of weekly cases for each state and dashed lines represent the smoothed number of cases using a fifth-order polynomial. (C) The second-order finite difference of the weekly case count for each state was used to calculate the beginning and end of the Lyme disease season for each state and year. The dotted lines in (A–C) represent the beginning week for each state.

Figure 2.

Percentage of statewide Lyme disease cases from 1992 to 2007 occurring in each county for the 12 highly endemic Lyme disease states included in our analysis. Dots represent the center of each state weighted by the county case percentages. State latitude and distance to the Atlantic coastline were calculated from these weighted centers.

Figure 3.

The overall mean beginning of the Lyme disease season from 1992 to 2007, along with the annual beginning weeks for three states: Minnesota, Connecticut, and Maryland.

Figure 4.

Beginning week of Lyme disease season across all states and years as a function of the cumulative growing degree days (GDD) above 10°C through Week 20 for that state and year (r² = 0.54).