Rocky Mountain Spotted Fever

Signs & Symptoms

Symptoms usually present in 2-14 days usually with a sudden onset of moderate to high fever, significant malaise, deep muscle pain, severe headache, chills and conjunctival infection. The "typical" triad of fever, rash, and tick bite are only presented between 21-40% of the time. Clinical signs and symptoms include:

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

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.

Diagnosis

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.

Antibodies
Antibodies to R. rickettsii are detectable 7-10 days after illness onset. The gold-standard serologic test looks for a four-fold change in antibody titers using immunofluorescence assay (IFA) on paired samples. The first sample should be taken within the first week of illness and the second should be taken 2 to 4 weeks later.

• Demonstration of a four-fold change in IgG-specific antibody titer by immunofluorescence assay (IFA) test in paired serum samples.
• Detection of DNA in a skin biopsy of rash by polymerase chain reaction (PCR) assay (generally unreliable for acute blood samples).
• Immunohistochemical (IHC) staining of organism.

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. For accurate testing of suspect cases an acute and convalescent serum are necessary.

Laboratory Findings
Common laboratory findings suggestive of RMSF include:

• Elevated liver enzyme levels
• Hyponatremia (reduced sodium levels)
• Thrombocytopenia (reduced platelet count)

Treatment

Doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever RMSF is suspected. Use of antibiotics other than doxycycline is associated with a higher risk of fatal outcome. Treatment is most effective at preventing death if doxycycline is started in the first 5 days of symptoms. Therefore, treatment must be based on clinical suspicion alone and should always begin before laboratory results return or symptoms of severe disease, such as petechiae, develop.

In Maricopa County

Although RMSF is not present in Maricopa County, there are still cases in residents who have traveled to endemic areas (both within and outside of the state) or moved from an endemic area. From 2006-2011 there were 56 cases investigated within Maricopa County. Of those investigated, one patient was a suspect case, four patients were probable cases, and one patient was confirmed for RMSF.