Pediatric Rocky Mountain Spotted Fever Workup

  • Author: Nicholas John Bennett, MB, BCh, PhD; Chief Editor: Russell W Steele, MD   more...
 
Updated: Aug 8, 2011
 

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. 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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Contributor Information and Disclosures
Author

Nicholas John Bennett, MB, BCh, PhD  Fellow in Pediatric Infectious Disease, Department of Pediatrics, State University of New York Upstate Medical University

Nicholas John Bennett, MB, BCh, PhD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Pediatrics

Disclosure: Nothing to disclose.

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, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Walid Abuhammour, MD, FAAP  Professor of Pediatrics, Michigan State University College of Medicine; Director of Pediatric Infectious Disease, Department of Pediatrics, Hurley Medical Center

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

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD  Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine

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, and Southern Medical Association

Disclosure: Nothing to disclose.

References

  1. 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. Mar 31 2006;55(RR-4):1-27. [Medline]. [Full Text].

  2. 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. Jul 2010;83(1):174-82. [Medline]. [Full Text].

  3. 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. Apr 2009;80(4):601-5. [Medline].

  4. 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. Jan 2009;80(1):72-7. [Medline].

  5. [Guideline] 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. Mar 31 2006;55:1-27. [Medline]. [Full Text].

  6. 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.

 
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Annual incidence per million population for Rocky Mountain spotted fever by state in the United States for 2002, as determined on the basis of cases reported to the National Electronic Telecommunications System for Surveillance. Image courtesy of the Centers for Disease Control and Prevention.
Table 1. Human Disease Around the World Caused by Spotted Fever Group Rickettsiae.
OrganismDisease or PresentationGeographic Location
Rickettsia rickettsiiRocky Mountain spotted feverNorth, Central and South America
Rickettsia conoriiMediterranean spotted fever, boutonneuse fever, Israeli spotted fever, Astrakhan fever, Indian tick typhusEurope, Asia, Africa, India, Israel, Sicily, Russia, Europe, Asia, Africa, India, Israel, Sicily, Russia
Rickettsia akariRickettsialpoxWorldwide
Rickettsia sibiricaSiberian tick typhus, North Asian tick typhusSiberia, People's Republic of China, Mongolia, Europe
Rickettsia australisQueensland tick typhusAustralia
Rickettsia honeiFlinders Island spotted fever, Thai tick typhusAustralia, South Eastern Asia
Rickettsia africaeAfrican tick-bite feverSub Saharan Africa, Caribbean
Rickettsia japonicaJapanese or Oriental spotted feverJapan
Rickettsia felisCat flea rickettsiosis, flea borne typhusWorldwide
Rickettsia slovacaNecrosis, erythema, lymphadenopathyEurope
Rickettsia heilongjaiangensisMild spotted feverChina, Asian region of Russia
Rickettsia parkeriMild spotted feverUS
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[6]
  • 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
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