Researchers began documenting tick-borne Lyme disease in the United States in 1991 when standardized surveillance and reporting began. Since that time, researchers have seen the number rise, according to a new study.

Ticks carrying Lyme disease are now in 1,531 (49.2%) counties spread across 43 states. This represents a 44.7% increase in the number of counties that have recorded the presence of these ticks since the previous map was presented in 1998.

The study, conducted by the Centers for Disease Control (CDC), was published in the Journal of Medical Entomology on Jan. 18.

Additionally, the number of counties in which I. scapularis is considered established has more than doubled since the previous national distribution map was published.

North-central and northeastern counties experienced changes in their tick status; southern state numbers remained fairly stable.

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