Rocky Mountain Spotted Fever

Agent
Rickettsia rickettsii

WHERE FOUND

Although Rocky Mountain spotted fever cases have been reported throughout most of the contiguous U.S., five states (North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri) account for over 60% of RMSF cases.

Rocky Mountain spotted fever has become increasingly common in certain areas of Arizona over the last several years. Between 2003 and 2012 over 250 cases and 19 fatalities occurred. RMSF can be rapidly fatal if not treated within the first 5 days of symptoms. Before tetracycline antibiotics were available, case fatality rates ranged from 20–80%.

INCUBATION PERIOD: 2-14 days

SIGNS AND SYPMTOMS

Localized Stage

• Fever, chills
• Severe headache
• Malaise
• Myalgia
• Gastrointestinal symptoms (nausea, vomiting, anorexia, abdominal pain, diarrhea, abdominal tenderness)
• Cough
• Photophobia
• Focal neurologic deficits, including cranial or peripheral motor nerve paralysis or sudden transient deafness

Maculopapular Rash

• Typically appears 2–5 days after the onset of fever
• Small, flat, pink, non-itchy spots (macules) initially appear on the wrists, forearms, and ankles then spread to the trunk and sometimes palms and soles.
• Rash may not develop until late in the disease process, after treatment should have already begun. Approximately 10% of RMSF patients never develop a rash at all.
• Consider RMSF if other signs and symptoms support a diagnosis, even if a rash is not present.

Petechial Rash

• Red to purple spots (petechiae) are usually not seen until day 6 or later after onset of symptoms.
• Petechial rash is considered a sign of progression to severe disease. Every attempt should be made to begin treatment before petechiae develop.

NOTE: Neurologic symptoms are typically not seen until later in the disease progression and may be prevented with early treatment.

Confirmation of the diagnosis is based on laboratory testing, but antibiotic therapy should not be delayed in a patient with a suggestive clinical presentation. Antibiotics are less likely to prevent fatal outcome from RMSF if started after day 5 of symptoms.

NOTE: IgM antibodies are less specific than IgG antibodies and are more likely to generate false positives. IgM results alone should not be used for laboratory diagnosis.

NOTE: Antibody titers are frequently negative in the first 7–10 days of illness, thus serologic tests may be falsely negative during this time period.

Treatment

Anaplasmosis, ehrlichiosis, and Rocky Mountain spotted fever are treated in the same manner with doxycycline.† Clinical suspicion of any of these diseases is sufficient to begin treatment. Delay in treatment may result in severe illness and even death. The regimens listed below are guidelines only and may need to be adjusted depending on a patient’s age, medical history, underlying health conditions, pregnancy status, or allergies. Consult an infectious disease specialist in cases of pregnancy or documented life-threatening allergies to doxycycline.

NOTE: Use doxycycline as the first-line treatment for suspected RMSF in patients of all ages. The use of doxycycline to treat suspected RMSF in children is recommended by both the CDC and the American Academy of Pediatrics Committee on Infectious Diseases. Use of antibiotics other than doxycycline increases the risk of patient death. At the recommended dose and duration needed to treat RMSF, no evidence has been shown to cause staining of permanent teeth, even when five courses are given before the age of eight.

References

†Biggs HM, Barton Behravesh C, 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 (2); 1-48.

Smithee L, et al. Public health reporting and national notification for spotted fever rickettsiosis [PDF – 96 KB] (including Rocky Mountain spotted fever). Council of State and Territorial Epidemiologists, Infectious Diseases Committee, 2009 Position Statement.

Todd SR, Dahlgren FS, et al. No visible dental staining in children treated with doxycycline for suspected Rocky Mountain spotted fever. J Pediatr, available online 17 March 2015.

Walker DH, Raoult D. Rickettsia ricketsii and other spotted fever group rickettsiae (Rocky Mountain spotted fever and other spotted fevers). In: Mandell GL, Bennett JE, Dolin R, editors. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, PA: Churchill Livingstone; 2005. p. 2287–2295.