CDC Reveals Lyme Disease Increase: Where to Next?

With ticks becoming more active as temperatures rise, so does the risk of Lyme disease. The Centers for Disease Control and Prevention (CDC) released a report revealing the increase of diagnoses over the past two decades in the US.

Caused by the bacterium Borrelia burgdorferi, Lyme disease is most commonly reported in northeastern, mid-Atlantic, and north-central states. While the tickborne zoonosis can be treated, it can cause joint pain, red rashes, and flu-like symptoms. The CDC assessed geographic distribution of the disease over 20 years in order to help determine future trends. The findings indicated that Lyme disease diagnoses are steadily increasing.

Level of Lyme disease incidences were defined using SaTScan software. The average population at risk in each county was calculated based on the US Census.

“Identification of high-risk clusters was based on county incidence rates,” the report explained, “with a maximum possible cluster size equal to 25% of the US population (minimum size was one country).”

Data on confirmed cases was collected from 1993 to 2012 and split into four sections for analysis.The number of counties with high Lyme disease incidences were revealed:

• 1993 — 1997: 69 counties
• 1998 — 2002: 130 counties
• 2003 — 2007: 197 counties
• 2008 — 2012: 260 counties

States in the northeast showed the largest increase of high incidences of more than 320%. Lyme disease cases were found to move westward and northward — away from northern New Jersey and into east-central Pennsylvania.

• 1993 — 1997: 43 counties
• 1998 — 2002: 90 counties
• 2003 — 2007: 130 counties
• 2008 — 2012: 182 counties

States in north-central experienced a jump of around 250% over the years. Lyme disease cases remained mainly in northwestern Wisconsin and moved northward and southward between close counties.

• 1993 — 1997: 22 counties
• 1998 — 2002: 40 counties
• 2003 — 2007: 67 counties
• 2008 — 2012: 78 counties

It was noted that four counties in the southeast had high incidence in the earlier years but improved over time which may be due to better detection. The team acknowledged several factors that could have influenced the data such as surveillance practices and resources; however, the method still provides a valuable way to pinpoint high risk counties for Lyme disease.

“Despite the substantial increase in the number of counties with high incidence, the limited movement of the geographic centers suggests relatively constant rates of geographic expansion in all accessible directions,” the report concluded.