Best Dx/Best Rx: Rocky Mountain Spotted Fever

Rocky Mountain Spotted Fever

Aurélie Renvoisé, MD
Didier Raoult, MD, PhD
Université de la Méditerranée, Marseille, France

An acute illness caused by Rickettsia rickettsii and transmitted by tick bite
Described in the western hemisphere
Abrupt onset
Incubation period after exposure: 2–14 days
Nonspecific symptoms of early phase (first 3 days) include fever, headache, malaise and myalgias, nausea and vomiting, and generalized or focal abdominal pain then fever and rash (macular)
Maculopapular skin eruption that develops 3–5 days after the fever and evolves into a generalized petechial rash; rash may be delayed or absent in some patients
Manifestations of severe disease include various neurologic manifestations, including deafness, convulsions, and hemiplegia; pulmonary and renal failure; myocarditis; and necrosis and gangrene of the fingers, toes, earlobes, and external genitalia

Differential Diagnosis

Other rickettsial diseases; typhus
Ehrlichiosis (distinguished from Rocky Mountain spotted fever [RMSF] by presence of severe leukopenia and absence of rash)
Bacterial sepsis; meningococcemia
Leptospirosis; typhoid fever
Measles; infectious mononucleosis; dengue; enterovirus infection
Hepatitis; gastroenteritis; bronchitis; pneumonia
Immune complex vasculitis; thrombotic thrombocytopenia, purpura
Drug eruption (especially if antibiotics such as ß-lactams are used as empirical therapy before the appearance of a typical skin rash)

Best Tests

Clinical Features

Diagnosis must be based on clinical features and epidemiologic setting; there is no completely reliable diagnostic test for RMSF in the early phases of illness; therapy must begin before laboratory confirmation is obtained

Laboratory Studies

Aminotransferases, bilirubin, and creatinine measurement: blood levels will be elevated in most patients, particularly those with severe illness
Serologic testing: no role in the initial diagnosis of acutely ill patients with suspected RMSF; antibodies do not appear before eighth to 10th day of illness
Diagnostic proof of RMSF can be obtained by direct detection (molecular testings or cell culture) in various samples (particularly skin biopsy) or, in the convalescent phase, by detection of specific antibodies
Molecular diagnosis and serum testing should be widely performed if the diagnosis is suspected
Cell culture requires specialized laboratory facilities available only at few centers
Lumbar puncture in patients with neurologic symptoms often shows a lymphocytic pleocytosis in the cerebrospinal fluid

Best Therapy*

Therapy should be initiated as early as possible; delays of > 5 days in the initiation of therapy are associated with fatal outcome

Antibiotics

Dosage: 100 mg q. 12 hr IV or p.o. (2.25–3 mg/kg/day for children) for 5–7 days (or until 2 days after the fever had subsided); IV preferred for patients who are seriously ill or who have nausea/vomiting

Chloramphenicol: alternative for pregnant women or those who cannot tolerate tetracyclines

Dosage: 50–75 mg/kg/day in 4 divided doses for 7 days or until 2 days after the fever had subsided

R. rickettsii is susceptible in vitro to fluoroquinolones, josamycin, and rifampin

Other Measures

Correct associated complications, such as septic shock and intravascular disseminated coagulation

Best References

Dantas-Torres. Lancet Infect Dis 2007;7:724. [PMID 17961858]

Kirkland KB, et al. Clin Infect Dis 1995;20:1118. [PMID 7619985]

Parola P, et al. Clin Microbiol Rev 2005;18:719–56. [PMID 16223955]

Rolain JM, et al. Antimicrob Agents Chemother 1998;42:1537–41. [PMID 9660979]

Paddock CD, et al. J Infect Dis 1999;179:1469. [PMID 10228069 ]

Kirk J, et al. Medicine (Baltimore) 1990;69:35. [PMID 2299975]

* To obtain additional drug information, click on the DrugInfo tab in the left column, or click on the following link: http://search.medscape.com/drug-reference-search?queryText=

November 2010