The geographic spread and temporal increase of the Lyme disease epidemic.

Objective: To describe the temporal and geographic progression of the Lyme disease epidemic in New York State from 1977 through 1989.

Design: Communicable disease surveillance system.

Setting: Statewide.

Main Outcome Measures: The progression of the epidemic was examined by analyzing trends in Lyme disease cases reported to the state surveillance system, town and county Lyme disease incidence rates, Lyme disease hospital discharge rates, and the distribution of Ixodes dammini ticks obtained from surveillance efforts and submitted for identification.

Main Results: The number of confirmed Lyme disease cases in New York has increased with concurrent increases in the number of hospital discharges. The number of counties endemic for Lyme disease increased from four to eight between 1985 and 1989. The number of counties with documented I dammini ticks increased from four in 1985 to 22 in 1989. Incidence of the disease also increased within known endemic counties.

Conclusions: Tick surveillance indicated that the range of I dammini has expanded annually into areas up to 384 km from the original known endemic areas of Long Island, NY, and Connecticut. Cumulative data from human surveillance resources document both temporal increases and geographic expansion of the Lyme disease epidemic in New York.