Spotted Fever Group Rickettsiosis: Reporting and Surveillance

DHS surveillance resources

• Case Reporting and Investigation Protocol (previously called EpiNet)—Spotted Fever Rickettsiosis P-01949 (PDF)
• Case Reporting and Investigation Protocol (previously called EpiNet)—Typhus Fever Group Rickettsiosis P-02251 (PDF)
• Wisconsin case report form for mail or fax.—Tickborne Rickettsial Disease Case Report, F-00336 (PDF)

Provider resources

• Rocky Mountain spotted fever symptoms, diagnosis, testing, and treatment from the CDC (Centers for Disease Control and Prevention)—Resources for Health Professionals
• A practical guide for health care and public health professionals from CDC—Diagnosis and Management of Tickborne Rickettsial Diseases:

Serologic testing

Paired serologic testing is a commonly available method for confirming recent SFGR. Serologic confirmation of SFGR requires demonstration of at least a fourfold change (for example, 1:64 to 1:256, or 1:128 to 1:512) in immunoglobulin G (IgG) specific antibody titer between paired acute and convalescent sera tested by indirect immunofluorescence assay (IFA).

• Collect the acute sample during the first week of illness. Collect the convalescent sample two to four weeks later, after the illness is resolved.
• IgG antibody titers are undetectable during the first week of illness in 85% of patients. Therefore, a negative test during this time doesn’t rule out infection.
• IgG antibody titers can remain elevated for many months after the disease has resolved.
• A single serologic test cannot confirm or rule out SFGR. At times, a single test leads to misinterpretation of results or misdiagnosis.
• Immunoglobulin M (IgM) antibody test results aren’t as reliable as IgG test results. IgM tests are less specific, and so they are more likely to produce a false positive result. IgM antibodies can persist for a long period of time, so positive IgM titers may not indicate acute infection. Single IgM antibody tests shouldn’t be used to diagnose SFGR.

Most commercial serologic assays are unable to distinguish one spotted fever group infection from another. Many pathogenic spotted fever group Rickettsia species share similar antigens. Antibodies directed to one of these antigens can cross-react with other spotted fever group antigens..

Other tests

These tests are less commonly available, but can help diagnose SFGR:

• Polymerase chain reaction (PCR)
• Immunohistochemical (IHC) assays
• Culture

PCR and culture on whole blood specimens obtained during the first several days of illness often are negative. Rickettsia rickettsii and other SFGR species don’t circulate in large numbers in blood until the disease has progressed to a severe phase. A positive PCR result is confirmatory. A negative PCR result cannot rule out diagnosis and shouldn’t be a reason to withhold treatment.

PCR or IHC assays can be performed on an eschar swab, if the patient has an eschar. Or it can be done on a skin biopsy, if the patient has a rash or eschar. See more details from the CDC’s Rickettsial Zoonoses Branch:

• Collecting an Eschar Swab
• Specimen Submission Guidelines

PCR, culture, and immunohistochemical assays can be performed on autopsy tissue.

Diagnosing SFGR, including Rocky Mountain spotted fever, can be difficult. Many of the signs and symptoms are non-specific during the early stages of illness and are similar to more common diseases.

Due to the severity of the Rocky Mountain spotted fever, providers should diagnose and treat patients with clinical suspicion of infection. Information on tick exposure can help with a diagnosis. This could include:

• A recent tick bite.
• Exposure to tick habitats.
• History of travel to areas with high incidence of disease.
• Contact with dogs.

Clinical lab findings can be used for confirmation. These may include:

• Thrombocytopenia.
• Lymphopenia.
• Leukopenia.
• Elevated liver enzymes.

Treatment decisions should be based on the patient’s history, and clinical signs and symptoms. The diagnosis of SFGR, including Rocky Mountain spotted fever, can be confirmed later using lab tests. Treatment should never be delayed while waiting for lab tests or withheld due to an initial negative test result.

Doxycycline is the antibiotic of choice for all SFGR, including Rocky Mountain spotted fever, for patients of all ages. Initiate treatment as soon as SFGR is clinically suspected. It’s important to treat patients as soon as possible after symptoms start.

Most people treated with oral antibiotics during the early stages of SFGR fully recover. Below are treatment recommendations for all SFGR, including Rocky Mountain spotted fever.

Treat patients for at least three days after the fever subsides and until there is evidence of clinical improvement. The minimum total course is five to seven days for uncomplicated cases.

Antibiotic treatment of asymptomatic patients following a tick bite isn’t recommended to prevent SFGR. There is no evidence this practice is effective, and it may only delay onset of disease.