Rocky Mountain spotted fever is a notifiable disease. Can be fatal if not treated early.
Doxycycline is the drug of choice for treatment in patients of all ages and is almost always curative, especially if given in the first 5 days of illness. As the risk of death rises if appropriate therapy is not started before the fifth day of illness, doxycycline should be prescribed for suspected disease before confirmatory diagnostic test results are available.
Signs and symptoms may be difficult to distinguish from those of common viral illnesses, leading to delayed diagnosis. Diagnosis should be considered in any person with a compatible clinical presentation and recent outdoor exposure.
A characteristic eschar or scab at the site of the tick bite is absent, in contrast to infections due to other tick-borne spotted fever group rickettsiae. A history of tick bite may not be elicited in up to nearly half of cases.
Rocky Mountain spotted fever (RMSF) is a systemic vasculitis caused by infection with Rickettsia rickettsii, a tick-borne, gram-negative, intracellular bacterium.Rickettsia rickettsii is one of the spotted fever group (SFG) rickettsiae and is closely related to the other group members by genetic and antigenic characteristics. It is the most frequently reported SFG rickettsial infection in North America and the most common fatal tick-borne infection in the US.Detailed content on other rickettsial infections is covered by our separate Rickettsial Diseases topic.
History and exam
Key diagnostic factors
- known recent tick exposure or bite
- triad of fever, rash, and history of tick exposure
- triad of fever, rash, and headache
- altered mental status
Other diagnostic factors
- abdominal pain
- residence in or recent exposure to rural area
- peripheral oedema
- illness onset in spring or summer
- returned travellers from an endemic area
- recent (within 2 weeks) outdoor exposure
- known antecedent tick bite
- exposure to dogs or pets that spend time outdoors
1st investigations to order
- serum electrolytes and urea
- indirect immunofluorescent antibody (IFA)
- blood culture
Investigations to consider
- complement fixation
- latex agglutination
- indirect haemagglutination
- enzyme immunoassay
- lumbar puncture
- convalescent serology
- chest x-ray
- abdominal CT scan
- polymerase chain reaction
suspected Rocky Mountain spotted fever
- Other rickettsial diseases
- CDC Health information for international travel (the Yellow Book): rickettsial diseases (including spotted fever & typhus fevers rickettsioses, scrub typhus, anaplasmosis, and ehrlichioses)
- Tickborne diseases of the United States: a reference manual for health care providers
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