Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 4 RMSF

Rocky Mountain Spotted Fever (RMSF)



  • Overall annual incidence rose from 1.7 to 7 cases per million in the United States between 2000 and 2007 (Openshaw 2010)
  • Annual incidence is highest in children aged 5-9 years of age (Amsden 2005)


  • Median age is 42 years of age with greater than 87% of cases reported in Caucasian patients (Openshaw 2010)


  • Slight male to female predominance (Openshaw 2010)

Morbidity/Mortality: RMSF is the most common fatal rickettsial illness in the United States

  • Overall hospitalization rates are noted be at 23.4% based on aggregated reviews of case reports (Openshaw 2010)
  • Case fatality rate is estimated to be 5-10% overall (Biggs 2016)
    • If treatment is delayed, case-fatality rates of 40-50% have been described for patients treated on day 8 or 9 of their illness
    • Case fatality rate is highest in those over the age of 70 (Amsden 2005)
    • Without treatment, the case fatality rate is over 25% (Lacz 2006)

Geography and Seasonality (Openshaw 2010): Cases have been found in all continuous 48 states

  • Five States account for over 64% of all reported cases:
    • North Carolina
    • Oklahoma
    • Arkansas
    • Tennessee
    • Missouri
  • Seasonal distribution is concentrated in June (38 %) and July (38%).
    • Second smaller peak is noted in October and November when adult ticks are active

Poor Prognostic Factors (Biggs 2016):

  • Age < 10 or > 40 years of age
  • Alcohol abuse
  • Glucose-6-phosphate dehydrogenase deficiency
  • Delays in diagnosis and treatment
  • Immunocompromised states
  • Use of sulfonamide antimicrobial

Pathogenesis (Lacz 2006):

  • Rickettsia has tropism for endothelial cells and is able to spread centripetally via filopodia propulsion.
  • Invasion of endothelial and smooth muscle cells of various organs leads to dysfunction of microcirculation, host immune response, vascular tone, angiogenesis, and normal hemostasis.
  • Multiple organ systems are infected including the brain, liver, skin, lungs, kidneys, as well as the gastrointestinal system.

History and Physical:

Symptoms (Biggs 2016):

  • Symptoms typically appear 3-12 days after bite of an infected tick
  • Classic Triad: Tick Bite, Rash, Fever
    • Present in only a minority of patients
  • Rash: Absence of rash does not rule out this diagnosis
    • Timeline:
      • Typically appears 2-4 days after fever onset
    • Distribution:
      • Begin on the ankles, wrists, and forearms and subsequently spreads to the palms, soles, arms, legs, and trunk
      • Typically spares the face
    • Morphology:
      • Day 1: Initially seen as small, blanching macules
      • Over next several days, the rash becomes maculopapular, sometimes exhibiting central petechiae
      • Day 5 and 6: Rash becomes primarily petechial with involvement of the palms and soles
    • Initial Symptoms (< 5 days):
      • Fever
      • Headache
      • Chills
      • Malaise
      • Myalgia
      • Photophobia
      • Conjunctival Suffusion
      • Periorbital and Peripheral Edema
      • Calf Pain
      • Acute Transient Hearting Loss
      • Gastrointestinal Symptoms
    • Severe Manifestations: Most cases are self-limiting, but RMSF has been associated with the following severe disease manifestations:
      • Meningoencephalitis, Coma, Cerebral Edema
      • Renal Failure
      • ARDS
      • Seizures
      • Shock
      • Cutaneous Necrosis and Gangrene
      • Arrhythmias, Myocarditis


Labs: Characteristic laboratory findings are seen in RMSF along fever and non-specific flu-like illness:

  • Thrombocytopenia
  • Hyponatremia
  • Mild Elevated Hepatic Transaminase
  • Increased Number of Immature Neutrophils

Confirmatory Testing (Dantas-Torres 2007):

  • Serological testing revealing four-fold change in IgG antibodies specific to R rickettsii using indirect immunofluorescence assay (IFA) in paired samples
    • Antibodies are not detected until 7-10 days after disease onset
  • RT-PCR assays are also available for diagnosis
  • ELISA testing is also available for diagnosis
  • Immunohistochemical staining from skin or tissue biopsies has also been used for diagnosis

Guest Post By:

Akash Ray, DO
PGY-2 Emergency Medicine Resident Inspira Medical Center
Vineland, NJ
Twitter: @_kashray


  1. Biggs H 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. PMID: 27172113
  2. Openshaw J et al. Rocky mountain spotted fever in the United States, 2000-2007: interpreting contemporary increases in incidence. Am J Trop Med Hyg. 2010. PMID: 20595498
  3. Amsden J et al. Tick-borne bacterial, rickettsial, spirochetal, and protozoal infectious diseases in the United States: a comprehensive review. Pharmacotherapy. 2005. PMID: 15767235
  4. Lacz N et al. Rocky Mountain spotted fever. J Eur Acad Dermatol Venereol. 2006. PMID: 16643138
  5. Dantas-Torres F. Rocky Mountain spotted fever. Lancet Infect Dis. 2007. PMID: 17961858

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

Cite this article as: Muhammad Durrani, "Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 4 RMSF", REBEL EM blog, November 5, 2020. Available at: https://rebelem.com/emerging-tick-borne-illnesses-not-just-lyme-disease-part-4-rmsf/.
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Muhammad Durrani

Assistant Clerkship Director & Assistant Research Director at Inspira Medical Center

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