1. Identify clinical presentation and diagnosis of Rocky Mountain spotted fever
ID: 260127 • Letter: 1
Question
1. Identify clinical presentation and diagnosis of Rocky Mountain spotted fever (RMSF) in patients with rapidly progressing febrile illness and recent exposure in northern Mexico, based on a series of 4 fatal cases.
2. Interpret the clinical course and management of RMSF in patients with rapidly progressing febrile illness and recent exposure in northern Mexico.
3. Determine the clinical implications of analysis of this series of 4 fatal cases of RMSF in patients with rapidly progressing febrile illness and recent exposure in northern Mexico.
Case 3 On 2 occasions in September 2014, a 39-year-old man sought care at a healthcare facility in Riverside County, California, for fever, cough, dyspnea, diarrhea, nausea, vomiting, and abdominal pain. Both times he was sent home with a suspected diagnosis of viral syndrome. His condition worsened, and he sought care at a third facility on day 3 of his illness, at which time leukopenia and thrombocytopenia were reported, and a chest radiograph showed pulmonary infiltrates suggestive of pneumonia; a mottled rash also appeared on his extremities. He was hospitalized and given vancomycin, imipenem, azithromycin, and metronidazole. Subsequently, he experienced respiratory failure, requiring ventilator assistance. On day 7, he was given doxycycline, and admitted to an intensive care unit. On day 16, he died. A plasma specimen obtained on day 7 revealed DNA of an SFGR species when tested by a real-time PCR at CDC (12). No autopsy was performed. The patient had frequently traveled to Mexicali; his most recent trip was 1 week before illness onset.Explanation / Answer
People with Rocky Mountain spotted fever (RMSF) generally present within a week after a tick bite. RMSF is a potentially lethal, but curable tick-borne disease, which was first described in Idaho in the 19th century. In 1906, Howard Ricketts demonstrated that RMSF was an infectious disease transmitted by ticks. Clinical presentation and diagnosis of RMSF requires culture and identification of R. rickettsii , which is the causal pathogen of RMSF. The clinical spectrum of human infection ranges from mild to fulminant disease. It does not grow in cell-free culture media, which requires living host cells like the yolk sac of embryonated eggs or cell culture. R. rickettsii is very small size (0.3 – 1.0 µm), which requires Gimenez or acridine orange stains for visualization on microscopy. Its cell wall contains peptidoglycan and lipopolysaccharide, similar to gram-negative bacteria. Further definitive diagnosis of RMSF requires serologic or tissue biopsy for more confirmation. A quicker laboratory diagnosis is achieved by immunohistochemical studies of skin biopsy samples if skin rashes are present. The IgM antibody levels should also be checked know the infection better.
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