Risk Factors:

Since 1991, when Lyme disease became a reportable disease, annual cases have doubled. (This increase is probably both due to increased infection rates as well as better diagnosis.) In general, about 25,000 cases of Lyme disease are now reported in the U.S. each year.

General Risk Factors

Anyone exposed to ticks is at risk for Lyme disease and other tick-borne diseases. Pets are also at risk. Naturally, anyone who is regularly outside in areas where tick rates are high has a greater than average risk for becoming infected.

Age. The highest reported incidence of Lyme disease occurs among children 5 - 14 years old and adults 45 - 54 years old.

Sex. Men and women are equally at risk.

The Risk for Lyme Disease after a Tick Bite

In general, the risk for developing Lyme disease after a tick bite is only 1 - 3%. The risk varies depending on different factors:

• The longer the tick has fed, the greater the risk.
• Nymph ticks carry a greater risk than adult ticks, probably because they are often too small to be detected (about the size of a pinhead). In addition, only nymph ticks that are at least partially swollen when removed pose any significant risk. (This suggests that they have feeding for a prolonged period.)

Geographic Locations

Locations in the U.S. Lyme disease has been reported in nearly all U.S. states. However, most Lyme disease cases are concentrated in the northeastern, mid-Atlantic, and north central states. Although Lyme disease was named for a town in Connecticut where the first American cases of the disease were described, in recent years Massachusetts, New Jersey, and Pennsylvania have reported the greatest number of cases.

Worldwide Locations. Pockets of Lyme disease exist around the world. The disease is common in Europe, particularly in forested areas of middle Europe and Scandinavia. The Borrelia family is also responsible for tick infections in Europe, but different subspecies (B. garinii and B. afzelii) may be more common there and cause slightly different symptoms. The infection has also been reported in Russia, China, and Japan.

High-Risk Landscapes

Deer ticks thrive in grassy areas that have low sunlight and high humidity. Woodlands and fields are prime habitats, but these ticks can also be found in the long grasses adjacent to beaches. The ticks are not confined to rural settings. In suburban areas, they can live in overgrown lawns, groundcover plants, and leaf litter.

Time of Year

The exact time of year for risk depends on a geographic region's seasons and how they affect the tick's breeding cycle. In general, the highest risk for Lyme disease onset is from June through August, and the lowest risk is from December through March.