Rocky Mountain spotted fever

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Última revisión: 12 Dec 2025

Última actualización: 27 Aug 2025

Rocky Mountain spotted fever (RMSF) can be fatal if not treated early.

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 one half of cases.

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.

Definición

RMSF is a systemic vasculitis caused by infection with Rickettsia rickettsii, a tickborne, gram-negative, intracellular bacterium.[1] Rickettsia rickettsii is one of the spotted fever group rickettsiae and is closely related to the other group members by genetic and antigenic characteristics. It is the most frequently reported spotted fever group rickettsial infection in North America and the most common fatal tickborne infection in the US.[2][3]

Anamnesis y examen

Principales factores de diagnóstico

known recent tick exposure or bite
triad of fever, rash, and history of tick exposure
triad of fever, rash, and headache
fever
rash
headache
nausea/vomiting
myalgia
altered mental status

Todos los datos

Otros factores de diagnóstico

abdominal pain
diarrhea
conjunctivitis
lymphadenopathy
peripheral edema
meningismus
splenomegaly
hepatomegaly
jaundice
seizures
shock
coma

Todos los datos

Factores de riesgo

illness onset in spring or summer
returned travelers from an endemic area
residence in or recent exposure to rural area
recent (within 2 weeks) outdoor exposure
known antecedent tick bite
exposure to dogs or pets that spend time outdoors

Todos los datos

Pruebas diagnósticas

Primeras pruebas diagnósticas para solicitar

CBC
serum electrolytes and blood urea nitrogen
LFTs
indirect immunofluorescent antibody (IFA)
blood culture

Todos los datos

Pruebas diagnósticas que deben considerarse

complement fixation
latex agglutination
indirect hemagglutination
microagglutination
enzyme immunoassay
lumbar puncture
chest x-ray
abdominal CT scan
immunohistochemistry
polymerase chain reaction

Todos los datos

Algoritmo de tratamiento

Inicial

suspected Rocky Mountain spotted fever (RMSF)

Colaboradores

Autores

Christopher A. Ohl, MD

Professor of Medicine

Section on Infectious Diseases

Wake Forest School of Medicine

Winston-Salem

Divulgaciones

CAO declares that he has no competing interests.

Agradecimientos

Professor Christopher A. Ohl would like to gratefully acknowledge Dr Steven C. Buckingham, a previous contributor to this topic. SCB is an author of several references cited in this topic. We were made aware that Dr Steven C. Buckingham is now deceased.

Revisores por pares

Mary Anne Jackson, MD

Chief

Section of Pediatric Infectious Diseases

Children's Mercy Hospital and Clinics

Professor of Pediatrics

University of Missouri-Kansas City School of Medicine

Kansas City

Disclosures

MAJ is an author of several references cited in this topic.

Peer reviewer acknowledgements

BMJ Best Practice topics are updated on a rolling basis in line with developments in evidence and guidance. The peer reviewers listed here have reviewed the content at least once during the history of the topic.

Disclosures

Peer reviewer affiliations and disclosures pertain to the time of the review.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

Biggs HM, Behravesh CB, Bradley KK, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever and other spotted fever group rickettsioses, ehrlichioses, and anaplasmosis - United States. MMWR Recomm Rep. 2016;65:1-44.Full text Abstract

Centers for Disease Control and Prevention. Ticks: tickborne diseases of the United States. Mar 2025 [internet publication].Full text

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials
- Other rickettsial diseases
- Meningococcemia
- Ehrlichiosis
More Differentials
Guidelines
- CDC Yellow Book: health information for international travel - rickettsial diseases
- Clinical care of Rocky Mountain spotted fever
More Guidelines
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Rocky Mountain spotted fever

Resumen

Definición

Anamnesis y examen

Principales factores de diagnóstico

Otros factores de diagnóstico

Factores de riesgo

Pruebas diagnósticas

Primeras pruebas diagnósticas para solicitar

Pruebas diagnósticas que deben considerarse

Algoritmo de tratamiento

suspected Rocky Mountain spotted fever (RMSF)

Colaboradores

Autores

Christopher A. Ohl, MD

Divulgaciones

Agradecimientos

Revisores por pares

Mary Anne Jackson, MD

Disclosures

Peer reviewer acknowledgements

Disclosures

References

Key articles

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials

Guidelines

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

Log in to access all of BMJ Best Practice