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Emergency And Acute Medicine – Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is a potentially life-threatening rickettsial infection characterized by invasion of small blood vessels, resulting in direct vascular injury and secondary immune-mediated vasculitis. The disease is caused by acute infection with Rickettsia rickettsii, transmitted by tick vectors. In the western United States, the primary vector is Dermacentor andersoni (wood tick), while in the eastern United States it is Dermacentor variabilis (dog tick). Although reported in all states, approximately half of cases occur in North Carolina, South Carolina, Tennessee, Oklahoma, and Arkansas. RMSF is more common from April through September but can occur year-round. It is more frequently seen in males and in individuals between 40 and 64 years of age.
The incubation period ranges from 2 to 14 days, with a median of 7 days. A history of tick bite within 14 days of rash onset is reported in about 60% of patients, though absence of a known tick bite does not exclude the diagnosis. Patients often report outdoor or rural exposure.
The hallmark finding is a characteristic rash that typically appears 3 to 5 days after symptom onset. Initially, the rash consists of small (1–4 mm), red, macular lesions that blanch with pressure. Over hours to days, lesions become darker, papular, and palpable. Within 2 to 3 days, the rash may become petechial or purpuric and may coalesce or ulcerate. In severe cases, necrosis of distal extremities can occur. Classically, the rash begins on the flexor surfaces of the wrists and ankles, spreads to the palms and soles, and then progresses centrally to involve the trunk and face. However, 10% of patients never develop a rash, and early in the illness the rash may be absent or subtle.
Systemic symptoms are common. Pulmonary findings may include nonproductive cough, chest pain, dyspnea, and rales. Gastrointestinal symptoms such as nausea, vomiting, abdominal pain, distention, ileus, and hepatosplenomegaly are frequent and may be associated with more severe disease due to widespread vasculitis. Neurologic involvement occurs in approximately two-thirds of patients and may include severe headache, meningismus, encephalitis, or focal deficits. Additional findings may include generalized edema, dehydration, malaise, myalgia, conjunctivitis, and retinal hemorrhages. Complications can include disseminated intravascular coagulation (DIC), noncardiogenic pulmonary edema, acute renal failure, and cardiovascular dysfunction. Mortality is higher in older adults, males, individuals with chronic alcohol abuse, African Americans, and those with glucose-6-phosphate dehydrogenase deficiency.
RMSF is primarily a clinical diagnosis supported by laboratory findings. Early laboratory abnormalities may include thrombocytopenia, anemia, and hyponatremia (often <130 meq />). Liver enzymes such as aspartate aminotransferase and lactate dehydrogenase may be elevated. White blood cell count is often normal. Coagulation studies may reveal abnormalities if DIC is present. Serologic testing confirms the diagnosis but is often negative in the first few days of illness. A single antibody titer greater than 1:64 or a fourfold rise in titers is diagnostic. Indirect immunofluorescence assay is the reference standard. Polymerase chain reaction testing and immunohistochemical staining of skin biopsy specimens may assist in diagnosis. CSF may show pleocytosis and elevated protein. Imaging such as chest radiography may demonstrate pulmonary edema or pneumonia in severe cases.
The differential diagnosis includes other tick-borne diseases such as ehrlichiosis, Lyme disease, tularemia, babesiosis, and Colorado tick fever, as well as meningococcemia, measles, rubella, varicella, viral exanthems, disseminated gonococcal infection, typhus, secondary syphilis, scarlet fever, Kawasaki disease, toxic shock syndrome, staphylococcal sepsis, allergic vasculitis, thrombotic thrombocytopenic purpura, and heat illness.
Management requires immediate initiation of antibiotic therapy based on clinical suspicion and epidemiologic factors. Treatment must not be delayed for laboratory confirmation, as early therapy significantly reduces mortality. Doxycycline is the drug of choice for both adults and children. The recommended dose is 100 mg orally or intravenously twice daily (2 mg/kg for children weighing less than 45 kg) for 5 to 7 days and continued for at least 2 to 3 days after defervescence. Despite prior concerns about dental staining, short courses of doxycycline are considered safe in children and are preferred due to the severity of untreated disease. Chloramphenicol is reserved for pregnant patients or those with severe allergy to doxycycline. Sulfonamides should be avoided, as they may worsen the infection.
Supportive care includes ABC management, intravenous fluid resuscitation with 0.9% normal saline for dehydration, oxygen therapy for hypoxia, correction of electrolyte abnormalities, and treatment of complications such as DIC, acute respiratory distress syndrome, or heart failure. Acetaminophen may be used for fever control. High-dose corticosteroids have been considered in severe cases with extensive vasculitis or cerebral edema, though their use remains controversial.
Patients with moderate to severe illness require hospital admission. Mild cases identified early and treated promptly may be managed as outpatients with close follow-up. Because cases may cluster and reflect shared environmental exposure, family members should be informed and evaluated if symptomatic.
Early recognition and empiric treatment based on clinical presentation and epidemiologic exposure are critical. Delayed therapy significantly increases morbidity and mortality, making prompt initiation of doxycycline the cornerstone of management.
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