Lyme disease is caused by the bacteria Borrelia burgdorferi, which is transmitted by the bite of infected Ixodes ticks. In the U.S., Lyme disease is common in the northeastern states, Atlantic coastal states, and the upper Midwest. Infections occur most often in late spring and summer when ticks are most prevalent. Generally, Lyme disease is uncommon in the Pacific Northwest. In Washington state it occurs primarily in the western half of the state.
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Purpose of surveillance:
- To detect cases and investigate associated environmental risk factors
- To facilitate appropriate diagnostic testing and treatment for infected persons
Six cases of Lyme disease were reported in 2012. Five had exposures outside of King County in endemic areas on the East Coast of the United States and one had exposure in Europe. An additional 56 reports were determined not to meet the criteria for a Lyme disease case.
Most cases thought to be acquired in Washington state have had outdoor exposure in counties west of the Cascade Mountains or in the Cascade foothills, where Ixodes ticks as well as their deer and rodent hosts are located.
Each year in Washington state there are fewer than 20 cases reported, and most are exposed outside Washington.