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Pediatric Rocky Mountain Spotted Fever Workup

  • Author: Nicholas John Bennett, MBBCh, PhD, MA(Cantab), FAAP; Chief Editor: Russell W Steele, MD  more...
 
Updated: Oct 25, 2015
 

Approach Considerations

Laboratory findings may be nonspecific in Rocky Mountain spotted fever (RMSF). On the complete blood count, the total leukocyte count may be normal, elevated, or decreased but usually shows a left shift.

Mild anemia and thrombocytopenia of less than 150 × 109/L (< 150 × 103/µL) occur in approximately one third of patients. Severe thrombocytopenia of less than 20 × 109/L (< 20 × 103/µL) occurs in approximately 10% of patients.

On a comprehensive metabolic panel, the following may be noted:

  • Hyponatremia (serum sodium < 130 mEq/L) in 20% of patients
  • The serum alanine aminotransferase level is usually increased
  • Serum albumin values may be low
  • The blood urea nitrogen (BUN) level is increased

Results of cerebrospinal fluid (CSF) analysis are generally normal. However, mild pleocytosis may be present, and approximately 50% of patients have a predominance of polymorphonuclear cells. An elevated CSF protein level may also be observed.

Serologic assays to detect anti– R rickettsii immunoglobulin G (IgG) antibodies are usually performed for definitive diagnosis.[8] Testing of acute-phase and convalescent-phase sera is recommended to demonstrate a 4-fold or higher increase in the titer.

Enzyme immunoassays (EIAs) and immunoglobulin M (IgM) antibody-capture immunoassays are new serologic tests that potentially allow for early diagnosis.

In research laboratories, isolation of rickettsiae from tissues or direct detection of rickettsiae in tissues by means of direct immunofluorescence is used to confirm the diagnosis. Polymerase chain reaction tests have been developed but are not widely available.

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Imaging Studies

CT imaging is typically normal, whereas MRI seems more sensitive at revealing abnormalities. Published findings include diffuse edema, effacement of the sulci, arterial infarctions, prominent perivascular spaces, and enhancement of the meninges (ie typical findings of meningoencephalitis). In 2 recent pediatric cases of Rocky Mountain spotted fever (RMSF) with encephalitis, scattered nonenhancing punctate lesions were described throughout the cerebral white matter, visible on T2- and diffusion-weighted MRI.[9, 10]

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Contributor Information and Disclosures
Author

Nicholas John Bennett, MBBCh, PhD, MA(Cantab), FAAP Assistant Professor of Pediatrics, Co-Director of Antimicrobial Stewardship, Medical Director, Division of Pediatric Infectious Diseases and Immunology, Connecticut Children's Medical Center

Nicholas John Bennett, MBBCh, PhD, MA(Cantab), FAAP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics

Disclosure: Received research grant from: Cubist Pharmaceuticals, Durata Therapeutics, and Biota Pharmaceutical<br/>Received income in an amount equal to or greater than $250 from: HealthyCT insurance<br/>Medico legal consulting for: Various.

Coauthor(s)

Joseph Domachowske, MD Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York Upstate Medical University

Joseph Domachowske, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa

Disclosure: Received research grant from: Pfizer;GlaxoSmithKline;AstraZeneca;Merck;American Academy of Pediatrics<br/>Received income in an amount equal to or greater than $250 from: Sanofi Pasteur;Astra Zeneca;Novartis<br/>Consulting fees for: Sanofi Pasteur; Novartis; Merck; Astra Zeneca.

Walid Abuhammour, MD, MBA, FAAP Professor of Pediatrics, Michigan State University College of Medicine; Director of Pediatric Infectious Disease, Department of Pediatrics, Al Jalila Children's Hospital

Walid Abuhammour, MD, MBA, FAAP is a member of the following medical societies: American Medical Association, Infectious Diseases Society of America, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Larry I Lutwick, MD Professor of Medicine, State University of New York Downstate Medical School; Director, Infectious Diseases, Veterans Affairs New York Harbor Health Care System, Brooklyn Campus

Larry I Lutwick, MD is a member of the following medical societies: American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

References
  1. McQuiston JH, Guerra MA, Watts MR, Lawaczeck E, Levy C, Nicholson WL, et al. Evidence of exposure to spotted fever group rickettsiae among Arizona dogs outside a previously documented outbreak area. Zoonoses Public Health. 2011 Mar. 58(2):85-92. [Medline].

  2. Chapman AS, Bakken JS, Folk SM, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis--United States: a practical guide for physicians and other health-care and public health professionals. MMWR Recomm Rep. 2006 Mar 31. 55(RR-4):1-27. [Medline]. [Full Text].

  3. Openshaw JJ, Swerdlow DL, Krebs JW, et al. Rocky mountain spotted fever in the United States, 2000-2007: interpreting contemporary increases in incidence. Am J Trop Med Hyg. 2010 Jul. 83(1):174-82. [Medline]. [Full Text].

  4. Centers for Disease Control and Prevention. Rocky Mountain Spotted Fever - Statistics and Epidemiology. Available at http://www.cdc.gov/rmsf/stats/. Accessed: January 27, 2013.

  5. Holman RC, McQuiston JH, Haberling DL, Cheek JE. Increasing incidence of Rocky Mountain spotted fever among the American Indian population in the United States. Am J Trop Med Hyg. 2009 Apr. 80(4):601-5. [Medline].

  6. Adjemian JZ, Krebs J, Mandel E, McQuiston J. Spatial clustering by disease severity among reported Rocky Mountain spotted fever cases in the United States, 2001-2005. Am J Trop Med Hyg. 2009 Jan. 80(1):72-7. [Medline].

  7. Folkema AM, Holman RC, McQuiston JH, Cheek JE. Trends in clinical diagnoses of Rocky Mountain spotted fever among American Indians, 2001-2008. Am J Trop Med Hyg. 2012 Jan. 86(1):152-8. [Medline]. [Full Text].

  8. McQuiston JH, Wiedeman C, Singleton J, Carpenter LR, McElroy K, Mosites E, et al. Inadequacy of IgM antibody tests for diagnosis of Rocky Mountain Spotted Fever. Am J Trop Med Hyg. 2014 Oct. 91 (4):767-70. [Medline].

  9. Maller VG, Agarwal AK, Choudhary AK. Diffusion imaging findings in Rocky Mountain spotted fever encephalitis: a case report. Emerg Radiol. 2012 Jan. 19(1):79-81. [Medline].

  10. Crapp S, Harrar D, Strother M, Wushensky C, Pruthi S. Rocky Mountain spotted fever: 'starry sky' appearance with diffusion-weighted imaging in a child. Pediatr Radiol. 2012 Apr. 42(4):499-502. [Medline].

  11. Centers for Disease Control and Prevention. Rocky Mountain Spotted Fever. Available at http://www.cdc.gov/rmsf/symptoms/index.html#treatment. Accessed: July 22, 2011.

  12. Todd SR, Dahlgren FS, Traeger MS, Beltrán-Aguilar ED, Marianos DW, Hamilton C, et al. No visible dental staining in children treated with doxycycline for suspected Rocky Mountain Spotted Fever. J Pediatr. 2015 May. 166 (5):1246-51. [Medline].

 
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Geographic distribution of Rocky Mountain spotted fever incidence in 2010, cases per million: Courtesy of the US Centers for Disease Control and Prevention.
Table 1. Human Disease Around the World Caused by Spotted Fever Group Rickettsiae.
Organism Disease or Presentation Geographic Location
Rickettsia rickettsii Rocky Mountain spotted fever North, Central and South America
Rickettsia conorii Mediterranean spotted fever, boutonneuse fever, Israeli spotted fever, Astrakhan fever, Indian tick typhus Europe, Asia, Africa, India, Israel, Sicily, Russia, Europe, Asia, Africa, India, Israel, Sicily, Russia
Rickettsia akari Rickettsialpox Worldwide
Rickettsia sibirica Siberian tick typhus, North Asian tick typhus Siberia, People's Republic of China, Mongolia, Europe
Rickettsia australis Queensland tick typhus Australia
Rickettsia honei Flinders Island spotted fever, Thai tick typhus Australia, South Eastern Asia
Rickettsia africae African tick-bite fever Sub Saharan Africa, Caribbean
Rickettsia japonica Japanese or Oriental spotted fever Japan
Rickettsia felis Cat flea rickettsiosis, flea borne typhus Worldwide
Rickettsia slovaca Necrosis, erythema, lymphadenopathy Europe
Rickettsia heilongjaiangensis Mild spotted fever China, Asian region of Russia
Rickettsia parkeri Mild spotted fever US
Table 2. Doxycycline Treatment for RMSF
  • Doxycycline is first-line treatment for both adults and children; antibiotics other than doxycycline increase the risk of death [11]
  • Dosage : for children < 45 kg (100 lb): 2.2 mg/kg body weight given twice a day
  • Dosage for adults: 100 mg every 12 hours
  • Treatment is most effective at preventing death if doxycycline is started within the first 5 days of symptoms; if treatment occurs within 5 days fever generally subsides within 24-72 hours
  • Patients should be treated for at least 3 days after the fever subsides and until there is evidence of clinical improvement; standard duration of treatment is 7-14 days - "Fever plus 3, at least a week"
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