A 25-year-old man presents with fever, rash starting on wrists and ankles then spreading to trunk, and history of tick bite. Weil-Felix test shows OX-19 and OX-2 agglutination but not OX-K agglutination. Specific serology (IFA) confirms Rickettsia rickettsii. What is the treatment of choice?
- A Chloramphenicol 500 mg four times daily for 7 days
- B Ciprofloxacin 500 mg twice daily for 7 days
- C Azithromycin 500 mg daily for 5 days
- D Doxycycline 100 mg twice daily for 7–10 days ✓
Explanation
Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii requires prompt treatment with doxycycline 100 mg twice daily, which is the drug of choice for ALL rickettsial infections including in children (despite dental staining concerns, the brief course is justified by the risk of fatality). The centrifugal rash beginning at wrists/ankles (with palms and soles involvement) spreading centrally is classic. In the Weil-Felix test, R. rickettsii agglutinates OX-19 and OX-2 Proteus strains (but not OX-K, which is specific for scrub typhus caused by Orientia tsutsugamushi).
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.