A 19-year-old man from Arizona is brought to the emergency department by his parents due to a high-grade fever, chills, and headache. He also complains of severe pain in the groin and axillary areas, which was preceded by swelling. Two days prior to this event, the patient's father was changing carpet in the patient's room and noticed a dead rat.
His temperature is 39.6 C (103.3 F), blood pressure is 100/70 mm Hg, and pulse is 98/min. Examination shows multiple severely tender, non-fluctuant, enlarged nodules in the axillary and groin regions. The skin over these areas is edematous and erythematous. Blood cultures are obtained.
Which of the following organisms is most likely responsible for this patient's infection?

Question

A 19-year-old man from Arizona is brought to the emergency department by his parents due to a high-grade fever, chills, and headache.  He also complains of severe pain in the groin and axillary areas, which was preceded by swelling.  Two days prior to this event, the patient's father was changing carpet in the patient's room and noticed a dead rat.
His temperature is 39.6 C (103.3 F), blood pressure is 100/70 mm Hg, and pulse is 98/min.  Examination shows multiple severely tender, non-fluctuant, enlarged nodules in the axillary and groin regions.  The skin over these areas is edematous and erythematous.  Blood cultures are obtained.
Which of the following organisms is most likely responsible for this patient's infection?

Quizplus · Accepted Answer

11ec193a_962e_7fc2_853d_111604183271_MD0002_00 This patient's presentation is consistent with infection by Yersinia pestis (bubonic plague), a gram-negative coccobacillus transmitted by infected fleas. The main Yersinia pathogens include Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis. Yersinia pestis causes plague, while the other two cause diarrheal illnesses. It is transmitted by infected fleas from rodents, scratches/bites from infected cats, eating contaminated food, direct handling of infected animals, and respiratory transmission from infected humans. Urban plague involves rats, which have been the major reservoir for human epidemics. Diagnosis requires high clinical suspicion in patients with travel to endemic areas (e.g., Southwestern US) or animal exposure, and unexplained fever with regional lymphadenitis. Diagnosis can be confirmed with blood cultures, fluid culture (e.g., bubo aspirate or CSF), peripheral blood smear (Wright-Giemsa stain) showing rod-shaped organisms, or serologic titers. Untreated disease can lead to bacteremia, multiorgan failure, and death in nearly 75% of patients. Suspected patients should be promptly treated with tetracyclines or streptomycin. Post-exposure prophylaxis with doxycycline is recommended for contact with known cases. (Choice A) Coccidioides immitis is endemic in the Southwestern United States. Patients usually have nonspecific systemic symptoms, dry cough, pneumonia, or skin lesions in the immunocompromised. This patient's regional lymphadenitis is not usually seen in coccidiomycosis. (Choice B) Francisella tularensis (tularemia) is transmitted via contact with infected animals (e.g., rabbits). Patients most commonly present with ulceroglandular disease with a single erythematous papular skin ulcer with central eschar, tender local lymphadenopathy, and sudden onset of systemic symptoms (e.g., fever, chills, etc.). (Choice C) Pasteurella multocida infection results from bites or scratches from domestic pets. Patients usually present with localized cellulitis within 24 hours, regional lymphadenopathy, and sometimes bacteremia with osteomyelitis, meningitis, or endocarditis. (Choice D) Streptobacillus moniliformis commonly causes rat bite fever. Patients usually present with fever, severe myalgias, asymmetrical arthralgias, and a fine macular rash. However, it usually does not cause regional lymphadenitis. Educational objective: Yersinia pestis infection causes the highly lethal bubonic plague and presents with swollen and painful lymph nodules and sudden onset of high-grade fever. Suspected patients should be treated rapidly with tetracyclines or streptomycin. Post-exposure prophylaxis with doxycycline is recommended for contact with known cases. __________ References: Humoral and cellular immune responses to Yersinia pestis infection in long-term recovered plague patients (http://www.ncbi.nlm.nih.gov/pubmed/22190397) Expression during host infection and localization of Yersinia pestis autotransporter proteins (http://www.ncbi.nlm.nih.gov/pubmed/21873491) Yersinia pestis--etiologic agent of plague. (http://www.ncbi.nlm.nih.gov/pubmed/8993858)

A 19-Year-Old Man from Arizona Is Brought to the Emergency