Rocky Mountain Spotted Fever Symptoms and Diagnosis
Rocky Mountain spotted fever symptoms may begin with fever, headache, or confusion
The rash can appear later or may not be obvious early
Prompt doxycycline treatment is critical
Rocky Mountain spotted fever symptoms can include fever, headache, rash, muscle pain, nausea, confusion, and other neurologic changes. Although RMSF was first identified in the Rocky Mountain region, cases are now reported throughout the United States, with higher incidence in the southeastern and south-central regions.
In their article, “Unconventional Rocky Mountain Spotted Fever Presentation From Kentucky: A Compelling Case Report and Literature Review,” Hussain and colleagues describe the case of a 71-year-old man who was admitted to the hospital with a fever, generalized weakness with myalgia, persistent hiccups, confusion, and agitation.1
A physical exam revealed that the patient exhibited tachycardia, tachypnea, elevated blood pressure, and a high fever of 103.3°F. Test results showed severe hyponatremia, leukocytosis, and abnormal blood parameters.
Initial treatment for sepsis
The man’s symptoms improved after he was treated with IV ceftriaxone for suspected sepsis due to a urinary tract infection or pneumonia.
However, the patient later developed a 106.5°F fever and was admitted to the ICU.
“Upon further history-taking to determine the source of a fever of unknown origin, the patient revealed a potential exposure to ticks and a cat suspected of having lice one week prior.”
He was subsequently tested for Bartonella, Borrelia burgdorferi, and Rickettsia, the bacterium that causes Rocky Mountain spotted fever.
As a precaution, the patient was treated empirically with doxycycline for a possible tick-borne illness and released from the hospital.
Although initial testing was inconclusive for a tick-borne illness, follow-up testing was positive for Rickettsia.
“This case report underscores the diagnostic challenges posed by atypical presentations of RMSF and emphasizes the critical importance of early detection and treatment to prevent severe complications.”
Why Rocky Mountain spotted fever is often misdiagnosed
Rocky Mountain spotted fever can be difficult to recognize early because the initial symptoms may resemble influenza, COVID-19, pneumonia, meningitis, urinary tract infection, gastroenteritis, or sepsis. In this case, the patient was initially treated for sepsis before tick exposure was recognized.
Recent reports continue to show that delayed recognition of RMSF can have serious consequences. In a 2024 MMWR report, six confirmed RMSF cases linked to exposure in Tecate, Mexico, were reported in California; three patients died. The authors emphasized that delayed diagnosis and delayed doxycycline treatment can lead to life-threatening outcomes.2
In an enhanced surveillance study from Sonora, Mexico, 510 RMSF cases were reported from 2015 through 2018, with a case-fatality rate of 44%. The mean time from symptom onset to doxycycline treatment was 7.9 days, and only 32% of treated patients received doxycycline within the first five days of illness.3
Neurologic symptoms of Rocky Mountain spotted fever
Neurologic symptoms may occur in Rocky Mountain spotted fever because the infection injures small blood vessels throughout the body, including vessels affecting the brain and nervous system. Symptoms may include confusion, agitation, disorientation, lethargy, stupor, seizures, meningitis, encephalitis, or coma in severe cases.
The Sonora surveillance study found that several severe manifestations were associated with fatal outcome, including disorientation, stupor, lethargy, shock, hemorrhage, jaundice, and seizures.3
These findings are clinically important because patients with RMSF may present with mental status changes before a classic rash is recognized. In patients with fever, confusion, recent tick exposure, dog exposure, or travel to an endemic region, RMSF should remain in the differential diagnosis.
Rocky Mountain spotted fever and rash
RMSF is often associated with rash, but the rash may be absent early in the illness or may develop after other symptoms have already progressed. In the Sonora surveillance study, rash was reported in 67% of cases overall and was more common in pediatric cases than adult cases.3
The absence of a rash should not exclude Rocky Mountain spotted fever when the clinical picture is concerning. Delaying treatment while waiting for rash development or confirmatory test results may increase the risk of severe complications.
Testing for Rocky Mountain spotted fever
Testing for Rocky Mountain spotted fever can be challenging early in the illness. Antibody testing may be negative during the first week because the immune response has not yet fully developed. PCR testing may be useful in selected patients, but treatment decisions should not depend on laboratory confirmation when RMSF is strongly suspected.
Laboratory abnormalities may include thrombocytopenia, hyponatremia, elevated liver enzymes, elevated creatinine, leukocytosis, leukopenia, or other signs of systemic illness. In the Sonora surveillance study, fatal cases had lower platelet counts and higher creatinine levels than nonfatal cases.3
Because RMSF can progress quickly, doxycycline is most effective when started early, ideally within the first five days of illness. Clinicians should not wait for confirmatory testing before treating a patient with compatible symptoms and epidemiologic risk.
Can a positive Rocky Mountain spotted fever test reflect a past infection?
Yes. Rocky Mountain spotted fever antibodies may remain detectable long after an infection has resolved, and serologic tests can also cross-react with other spotted fever group rickettsiae. As a result, a single positive antibody test does not necessarily indicate active Rocky Mountain spotted fever.
In my clinical practice, I occasionally evaluate patients with positive RMSF serology who do not recall a classic acute febrile illness. These findings should be interpreted in the context of the patient’s symptoms, exposure history, timing of testing, and, when available, paired acute and convalescent antibody titers.
Rocky Mountain spotted fever key points
- RMSF typically manifests with vague symptoms, including fever, headache, rash, muscle pain, nausea, and malaise.
- Some patients develop neurologic symptoms, including confusion, agitation, disorientation, lethargy, stupor, seizures, or coma.
- Early laboratory test results may be normal or inconclusive.
- Confirmatory diagnostic results may take time, and antibody testing can be negative early in the illness.
- A single positive RMSF antibody test does not always prove active infection.
- Doxycycline should be started promptly when RMSF is clinically suspected.
- RMSF may be mistaken for sepsis, pneumonia, viral illness, meningitis, urinary tract infection, or gastroenteritis.
Frequently Asked Questions
Can Rocky Mountain spotted fever occur without a rash?
Yes. Although many patients with Rocky Mountain spotted fever develop a rash, it may be absent early in the illness or may never be recognized. The absence of a rash should not delay treatment when RMSF is suspected.
Can Rocky Mountain spotted fever cause confusion?
Yes. Rocky Mountain spotted fever can cause neurologic symptoms such as confusion, agitation, disorientation, lethargy, stupor, seizures, meningitis, encephalitis, or coma in severe cases.
Can Rocky Mountain spotted fever be mistaken for sepsis?
Yes. Early RMSF may resemble sepsis, pneumonia, urinary tract infection, meningitis, influenza, COVID-19, or gastroenteritis because the early symptoms are often nonspecific.
Can a positive Rocky Mountain spotted fever test mean past exposure?
Yes. RMSF antibodies may remain detectable after a past infection, and serologic tests can cross-react with other spotted fever group rickettsiae. A single positive antibody test should be interpreted with the clinical history, exposure risk, timing of illness, and, when available, paired antibody titers.
Should Rocky Mountain spotted fever treatment wait for test results?
No. Treatment should not wait for confirmatory testing when RMSF is clinically suspected. Early antibody testing may be negative, and delayed doxycycline treatment can increase the risk of severe complications and death.
Clinical Takeaway
Rocky Mountain spotted fever can present with nonspecific symptoms such as fever, muscle pain, headache, nausea, confusion, agitation, or sepsis-like illness before a classic rash is recognized.
Testing can support the diagnosis, but early results may be negative or inconclusive. A single positive antibody test may reflect past exposure or cross-reactivity rather than active infection.
Because severe complications can develop quickly, clinicians should consider RMSF in patients with compatible symptoms and possible tick exposure, dog exposure, or travel to an endemic region.
When Rocky Mountain spotted fever is clinically suspected, early doxycycline treatment should not be delayed while waiting for confirmatory laboratory testing.
Related Articles
These related articles explore tick-borne infections, severe presentations, and diagnostic challenges:
Tick bite leads to Rocky Mountain spotted fever
Fatal case of Heartland Virus
Ehrlichiosis and Lyme disease
Babesia and Lyme disease
Lyme disease misdiagnosis
References
- Hussain A, Gray C, Marlowe S, et al. Unconventional Rocky Mountain Spotted Fever Presentation From Kentucky: A Compelling Case Report and Literature Review. Cureus. 2023;15(11):e48558. doi:10.7759/cureus.48558
- Kjemtrup AM, Hacker JK, Monroe M, et al. Severe and Fatal Rocky Mountain Spotted Fever After Exposure in Tecate, Mexico — California, July 2023–January 2024. MMWR Morb Mortal Wkly Rep. 2024;73(47):1069-1075. doi:10.15585/mmwr.mm7347a1
- Álvarez-López DI, Ochoa-Mora E, Heitman KN, et al. Epidemiology and Clinical Features of Rocky Mountain Spotted Fever from Enhanced Surveillance, Sonora, Mexico: 2015–2018. Am J Trop Med Hyg. 2021;104(1):190-197. doi:10.4269/ajtmh.20-0854
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
In my twenties I had Rocky Mountain Spotted Fever from a nymph tick in New Jersey in 1989. It was undiagnosed til I went to a party with an infectious disease doctor who confirmed it. In my fifties I came down with four autoimmune diseases and two connective tissue diseases and now I’m quite sure I’m dealing with a Lysosomal Dusirder, Gaucher or Fabry Diseases as I also have POTS and EDS.
I had RMSF and went into psychosis from it. I was placed in an emergency psych facility for a week and my life fell apart as a result. My spouse divorced me and I lost my home and job. Doctors told me to apply for SSDI but I would have been homeless. I also have Hashimotos Encephalopathy so perhaps that triggered an autoimmune attack. I had a petachaie type rash on my chest and torso, stomach problems, myalgia, weakness, fatigue and joint pain, and also random fevers and mental confusion. I have tested positive twice for this despite being on Doxycycline. I now am on the Buehner protocol for it and feel great most days, most symptoms gone. If you think you have Lyme make sure to get on Doxycycline and the Buehner protocols as they will treat RMSF