WBR0297

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [2])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 40-year-old man presents to the emergency department (ED) with complaints of headache, fever, vomiting, and a rash. He explains that he first had vomiting and headaches 5 days ago, but then developed a high-grade fever and rash. He also states that the rash started over his wrists and ankles, but then proceeded towards his trunk. Upon further questioning, the patient informs the physician that he has recently traveled to North Carolina to visit his relatives and went camping there for several days. In the ED, his temperature is 38.9 °C (102 °F), blood pressure is 132/86 mmHg, and heart rate is 102/min. Physical examination is remarkable for multiple, non-blanching petechiae over the trunk and extremities with involvement of the palms and soles. Which of the following organisms is responsible for this patient's symptoms?]]
Answer A	[[AnswerA::Coxiella burnetti]]
Answer A Explanation	[[AnswerAExp::Coxiella burnetti causes Q fever and does not manifest with a rash.]]
Answer B	[[AnswerB::Rickettsia typhi]]
Answer B Explanation	[[AnswerBExp::Rickettsia typhi often results in endemic typhus. It is transmitted by fleas and manifests with a rash that typically originates at the trunk.]]
Answer C	[[AnswerC::Rickettsia rickettsii]]
Answer C Explanation	[[AnswerCExp::Rocky mountain spotted fever (RMSF) is caused by Rickettsia rickettsii]]
Answer D	[[AnswerD::Ehrlichia chaffeensis]]
Answer D Explanation	[[AnswerDExp::Ehrlichia chaffeensis is also transmitted by ticks. However, it does not manifest with a rash. It often leads to Ehrlichiosis and typically causes thrombocytopenia and leukopenia.]]
Answer E	[[AnswerE::Rickettsia prowazekii]]
Answer E Explanation	[[AnswerEExp::Rickettsia prowazekii ofetn causes epidemic typhus and manifests with a rash that originates at the trunk.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Rocky mountain spotted fever (RMSF) is caused by Rickettsia rickettsii, an obligate intracellular bacteria that is carried by ticks (eg. wood tick or American dog Dermacentor variabilis tick) and spread to humans by tick bites. Despite its name, RMSF is common in southeastern and southcentral USA (North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri) especially during the spring and summer. The disease is often characterized by a prodrome of non-specific GI symptoms, headaches, and myalgias followed by a fever and a rash. The rash has a centripetal distribution, where it initially manifests as small, blanching, maculopapular lesions over the distal upper and lower extremities (wrists and ankles) with involvement of the palms and soles and then progresses centrally to include the trunk with petechial, hemorrhagic, and non-blanching features. Educational Objective: Rocky Mountain spotted fever (RMSF) is caused by Rickettsia rickettsii. RMSF first manifests with non-specific GI symptoms followed by fever and a rash. The rash is often initially described as a maculopapular rash over the distal upper and lower extremities (wrists and ankles) with involvement of the palms and soles, but soon progresses to involve the trunk. References: Helmick CG, Bernard KW, D'Angelo LJ. Rocky Mountain spotted fever: clinical, laboratory, and epidemiological features of 262 cases. J Infect Dis. 1984;150(4):480-8. First Aid 2014 page 144]]
Approved	Approved::Yes
Keyword	WBRKeyword::Rash, WBRKeyword::Rickettsia rickettsii, WBRKeyword::Rickettsia, WBRKeyword::RMSF, WBRKeyword::Infection, WBRKeyword::Camping, WBRKeyword::Rocky Mountain spotted fever, WBRKeyword::Fever, WBRKeyword::North Carolina, WBRKeyword::Dermacentor variabilis, WBRKeyword::American dog tick, WBRKeyword::Tick, WBRKeyword::Tickborne disease, WBRKeyword::Vector
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