Rickettsial Diseases — Scrub Typhus, RMSF

A 32-year-old farmer from Tamil Nadu presents with fever, headache, and myalgia for 8 days. On examination, a painless eschar is noted on the left axilla with regional lymphadenopathy. Peripheral blood shows thrombocytopenia and elevated transaminases. Which investigation is most appropriate for rapid confirmation of scrub typhus?

A 28-year-old male agricultural worker from Tamil Nadu presents with a 7-day history of fever, severe headache, and myalgia. On examination, he has a temperature of 39.5°C, a maculopapular rash over the trunk and limbs, and a small black eschar with surrounding erythema on his left thigh. His WBC count is 8,500/μL with relative lymphocytosis. Platelet count is 95,000/μL. Liver enzymes are mildly elevated (AST 78 U/L, ALT 65 U/L). What is the most likely diagnosis?

A 42-year-old woman from North Carolina, USA, presents with a 5-day history of fever (39.8°C), severe headache, and myalgia. On examination, she has a petechial rash that began on her wrists and ankles 2 days ago and has now spread to involve the trunk, palms, and soles. She is hypotensive (BP 100/65) and tachycardic (HR 118/min). Laboratory findings show WBC 12,000/μL, platelets 45,000/μL, and elevated transaminases (AST 156 U/L, ALT 132 U/L). A skin biopsy shows vasculitis with rickettsiae within endothelial cells. What is the most likely diagnosis?

A 28-year-old woman from Himachal Pradesh presents with fever, rash on wrists and ankles spreading centripetally, and thrombocytopenia (platelet count 75,000/μL). Blood culture and PCR for scrub typhus are negative. Which finding would most strongly support a diagnosis of Rocky Mountain spotted fever over scrub typhus?

A 28-year-old woman from Himachal Pradesh presents with a 7-day history of fever, severe headache, myalgia, and rash on the wrists and ankles. On examination, petechial rash is noted on the flexor surfaces. She has no eschar. Platelet count is 92,000/μL, and serum creatinine is 1.8 mg/dL. Blood cultures are pending. She reports tick exposure while hiking 10 days ago. What is the most appropriate next step?