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Rocky Mountain spotted fever (RMSF) is a severe tick-borne infection caused by the bacterium Rickettsia rickettsii. R. rickettsii is transmitted via infected ticks, most commonly by the species Dermacentor. These 'hard ticks' are typically found in the western, south, and southeast regions of Washington state, however RMSF is uncommon. Activities that increase contact with ticks include hiking or walking in wooded and dense brush areas, meadows, and in areas with weeds and tall grass. Over half of the nationally reported cases occur in the south-Atlantic region of the United States.


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Rocky Mountain Spotted Fever in King County

Purpose of surveillance:

  • To detect cases of rare and emerging diseases
  • To understand the epidemiology of rare and emerging diseases

Local epidemiology:

The last reported case of RMSF occurred in 2008; the person reported travel to eastern Washington state and Yellowstone, WY. Each year in Washington state between zero and two cases are reported.