WBR0060

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category	SubCategory::Dermatology, SubCategory::General Principles, SubCategory::Infectious Disease
Prompt	[[Prompt:: A 34-year-old woman presents to her physician's office complaining of a rash that started on her palms and soles but has begun spreading to her wrists and ankles. She has been experiencing headaches, malaise and progressive fever. She does not drink or smoke, but is sexually active. She reports no international travel but recently returned from a vacation on Cape Cod. What is the proper treatment for the most likely causal organism?]]
Answer A	AnswerA::Doxycycline
Answer A Explanation	AnswerAExp::'''Correct:''' Rocky mountain spotted fever is caused by Rickettsia ricketssii and is treated with doxycycline.
Answer B	AnswerB::Erythromycin
Answer B Explanation	AnswerBExp::'''Incorrect:''' Erythromycin is a macrolide antibiotic which blocks ribosomal translocation. It is used for atypical pneumonias such as mycoplasma infections.
Answer C	AnswerC::Ampicillin
Answer C Explanation	AnswerCExp::'''Incorrect:''' Ampicillin is an extended spectrum Beta-lactamase that helps to kill enterococci.
Answer D	AnswerD::Trimethoprim-Sulfamethoxazole
Answer D Explanation	AnswerDExp::'''Incorrect:''' TMP-SMX (Bactrim) inhibits bacterial folate synthesis and is most commonly used for urinary tract infections
Answer E	AnswerE::Cephalexin
Answer E Explanation	AnswerEExp::'''Incorrect:''' Cephalexin is a first generation cephalosporin which is also a beta-lactam based drug and inhibits cell wall synthesis. It is most commonly used against gram positive cocci.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient in this vignette has been infected with Rickettsia ricketssii, which causes Rocky mountain spotted fever. Patients with Rocky mountain spotted fever are infected with the Rickettsial organism through Dermacentor tick bites. Despite the syndrome's name, Rickettsia ricketssii is endemic to the east coast. A hallmark of infection is a rash starting at the palms and soles that extends to the wrists and ankles over time. Very few organisms cause rash on the palms and soles, only Coxsackie A, Rickettsia Rickettssi and Syphilis (think CARS). Rocky mountain spotted fever can be diagnosed by a Weil-Felix test in which patient serum is incubated with Proteus antigens and agglutination is considered a positive test. Finally, all Rickettsia are intracellular organisms which require CoA and NAD+, and all infections are treated with doxycycline, a tetracycline antibiotic which inhibits 30S ribosome binding to aminoacyl-tRNA. Educational Objective: Rocky mountain spotted fever is treated with doxycycline. References: First Aid 2014 page 144 First Aid 2012 page 168 Tags: #Microbiology #Pharmacology Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Zoonotic, WBRKeyword::Animal, WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Rocky mountain spotted fever, WBRKeyword::Pharmacology, WBRKeyword::Antibiotics, WBRKeyword::Drugs
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