Lyme Disease and Related Tick-Borne Infections - Risk Factors

Highlights	Diseases with Similar Symptoms	Babesiosis
Introduction	Diagnosis	Resources
Symptoms	Treatment	References
Risk Factors	Prevention
Complications	Ehrlichiosis

Risk Factors

The Centers for Diseases Control (CDC) reports that more than 145,000 Lyme disease cases have been diagnosed since 1982. Reports of Lyme disease cases in the U.S. peaked in 2002 when nearly 24,000 cases were reported that year. Lyme disease is now the most common vector-borne disease in America. (Vector-borne infections are those that are transmitted by insects.)

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.

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Age. In the U.S., the highest reported incidence of Lyme disease occurs among children 5 to 9 years old and adults 50 to 59 years old.

Gender. The reported incidence is higher for females than for males. The gender discrepancy may be attributable to increases in the following:

Exposure to infected ticks
Less use of personal protective measures
Men may tend to report symptoms less often than women

The Risk for Lyme Disease After a Tick Bite

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

The longer the tick has fed the greater the risk. In fact, in one study, no individuals developed Lyme disease after being bitten by a nymph tick for less than 72 hours. In those on whom the tick had been feeding for longer than that, the risk was 25%.
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.In 2002, Lyme disease was reported in all states except Hawaii, Montana, and Oklahoma. However, nearly all of Lyme disease cases are concentrated in three regions:

In northeastern states from Maine to Maryland.
Two northcentral states (Minnesota and Wisconsin)
In the northwest (California and Oregon)

In such areas, between 1 - 3% of people who live there become infected at some time. New York has had the highest number of total cases to date, followed by Connecticut, which actually has the highest number of infected patients per total population. Pennsylvania and New Jersey have the next highest infection rates.