Infectious Disease · Rickettsial Infections
The facts most likely to be tested
Rocky Mountain Spotted Fever is caused by the intracellular bacterium Rickettsia rickettsii and is transmitted by the Dermacentor variabilis (American dog tick).
The classic clinical triad consists of fever, headache, and a centripetal rash that begins on the wrists and ankles before spreading to the trunk.
The characteristic petechial rash typically appears on the palms and soles in the later stages of the disease.
Diagnosis is primarily clinical because serologic testing (e.g., IFA) is often negative during the first week of illness.
Empiric treatment with doxycycline must be initiated immediately upon clinical suspicion to prevent multi-organ failure and death.
Doxycycline is the first-line treatment for all patients, including children and pregnant women, as the benefits of preventing severe disease outweigh the risks of dental staining.
Untreated infection leads to vasculitis resulting in severe complications such as thrombocytopenia, hyponatremia, and elevated transaminases.
Vignette unlocked
A 12-year-old boy is brought to the emergency department with a 4-day history of high-grade fever, severe frontal headache, and malaise. His mother reports he recently returned from a camping trip in North Carolina. Physical examination reveals a maculopapular rash involving the wrists and ankles that has begun to spread to his palms. Laboratory studies are significant for thrombocytopenia and hyponatremia.
What is the most appropriate next step in management?
Initiate empiric treatment with doxycycline
The patient presents with the classic triad and rash distribution of Rocky Mountain Spotted Fever; immediate treatment with doxycycline is required to prevent mortality, regardless of the patient's age.
Full handout
High yield triage
Etiology / Epidemiology
Caused by Rickettsia rickettsii, transmitted by the Dermacentor tick. Endemic in Southeastern/South Central US.
Clinical Manifestations
Triad of fever, headache, and rash. Rash starts on wrists/ankles and spreads centripetally.
Diagnosis
Indirect fluorescent antibody (IFA) is the gold standard. Clinical diagnosis is mandatory before labs return.
Treatment
Doxycycline is the first-line treatment for all ages. Do not delay treatment for diagnostic testing.
Prognosis
High mortality if untreated. 5-10 days is the critical window for intervention to prevent multi-organ failure.
Full handout
Epidemiology & Etiology
Transmitted by the Dermacentor variabilis (dog tick) and Dermacentor andersoni (wood tick). Most cases occur in the spring and summer months. High-risk regions include North Carolina, Tennessee, Oklahoma, Arkansas, and Missouri.
Pertinent Anatomy
The pathogen targets vascular endothelial cells throughout the body. This systemic infection leads to widespread vasculitis affecting the skin, lungs, brain, and kidneys.
Pathophysiology
The bacteria invade the vascular endothelium, causing increased vascular permeability and microvascular leakage. This leads to hypovolemia and edema. The resulting vasculitis is responsible for the characteristic petechial rash and potential for end-organ ischemia.
Clinical Manifestations
Initial symptoms include fever, malaise, and severe headache. The classic petechial rash begins on the wrists and ankles 2-5 days after fever onset, spreading centripetally to the trunk. Palms and soles involvement is a late, highly specific finding. Altered mental status and seizures indicate severe neurological involvement.
Diagnosis
Diagnosis is clinical; do not wait for serology. The Indirect fluorescent antibody (IFA) assay is the gold standard, but results are often delayed. Labs may show thrombocytopenia, hyponatremia, and elevated transaminases.
Treatment
Doxycycline is the mandatory first-line treatment for all patients, including children. Avoid chloramphenicol due to severe toxicity. Treatment must be initiated within the first 5 days of symptoms to significantly reduce mortality.
Prognosis
Untreated disease leads to multi-organ failure and death. Survivors may suffer from permanent neurological deficits or limb amputations due to severe vasculitis. Close monitoring for pulmonary edema and seizures is required.
Differential Diagnosis
Meningococcemia: presents with nuchal rigidity and purpura fulminans
Measles: rash starts on face and spreads downward, involves palms/soles
Secondary Syphilis: rash involves palms/soles but is usually non-tender and copper-colored
Ehrlichiosis: similar tick-borne presentation but typically lacks the classic petechial rash
Kawasaki Disease: prolonged fever >5 days with conjunctivitis and strawberry tongue