A 66-year-old man comes to the hospital due to 2 days of fever, chills, fatigue, and malaise. He has had no chest pain, cough, diarrhea, or dysuria. The patient has a history of lymphoma and underwent a splenectomy 6 years ago. Prior to the splenectomy, he received vaccinations against Neisseria meningitidis and Streptococcus pneumoniae. Six months ago, the patient returned from a 2-week trip to India during which he did not take antimalarial prophylaxis. He has no known ill contacts. The patient lives in Massachusetts and is a professor at a local college.
Temperature is 38.6 C (101.5 F), blood pressure is 122/70 mm Hg, and pulse is 110/min and regular. The patient has mild respiratory distress. The oropharynx is dry without lesions. Lung examination reveals bilateral coarse crackles. The abdomen is soft and mildly tender throughout. He has no skin rash.
Laboratory results are as follows:

A chest x-ray reveals diffuse bilateral infiltrates. A peripheral blood smear shows intraerythrocytic inclusions (see exhibit).
Which of the following is the most likely organism causing this patient's illness?

Question

A 66-year-old man comes to the hospital due to 2 days of fever, chills, fatigue, and malaise.  He has had no chest pain, cough, diarrhea, or dysuria.  The patient has a history of lymphoma and underwent a splenectomy 6 years ago.  Prior to the splenectomy, he received vaccinations against Neisseria meningitidis and Streptococcus pneumoniae.  Six months ago, the patient returned from a 2-week trip to India during which he did not take antimalarial prophylaxis.  He has no known ill contacts.  The patient lives in Massachusetts and is a professor at a local college.
Temperature is 38.6 C (101.5 F), blood pressure is 122/70 mm Hg, and pulse is 110/min and regular.  The patient has mild respiratory distress.  The oropharynx is dry without lesions.  Lung examination reveals bilateral coarse crackles.  The abdomen is soft and mildly tender throughout.  He has no skin rash.
Laboratory results are as follows:

A chest x-ray reveals diffuse bilateral infiltrates.  A peripheral blood smear shows intraerythrocytic inclusions (see exhibit).
Which of the following is the most likely organism causing this patient's illness?

Quizplus · Accepted Answer

11ec193a_986b_77fd_853d_47ac2dc93080_MD0002_00 This patient with a history of splenectomy lives in Massachusetts and presents with an abrupt onset of febrile illness associated with acute kidney injury, respiratory distress, and thrombocytopenia. The peripheral blood smear demonstrates intraerythrocytic ring forms with tetrads, termed the "Maltese cross," a distinguishing feature of babesiosis. Patients with splenectomy are at high risk for severe Babesia infection, which can manifest as congestive heart failure, acute respiratory distress syndrome, or disseminated intravascular coagulation, among other conditions. Maltese cross (Choice A) Anaplasma phagocytophilum is the causative agent of human granulocytic anaplasmosis (HGA). Although the risk factors for anaplasmosis are similar to those of babesiosis and both are carried by the same tick vector (Ixodes scapularis), the peripheral smear in HGA typically shows intracytoplasmic inclusions in granulocytes. (Choice C) Borrelia burgdorferi is the spirochete that causes Lyme disease. Intraerythrocytic organisms would not be seen with Lyme disease. (Choice D) Ehrlichia chaffeensis is a causative agent of human monocytic ehrlichiosis, a tickborne disease in which ehrlichiae infect monocytes, not erythrocytes. (Choice E) Although the patient traveled to a malaria-endemic area and did not take prophylaxis, the presence of Maltese cross tetrads and the absence of schizonts, gametocytes, and malarial pigment on the blood smear distinguish babesiosis from malaria. Furthermore, the incubation period for plasmodium malaria is typically 1-2 weeks, so presentation >3 months following exposure would be unusual. Educational objective: The diagnosis of babesiosis can be established based on identification of organisms on a thin blood smear (intraerythrocytic ring forms with Maltese cross tetrads). Patients with a history of splenectomy are at risk for severe illness. __________ References: Babesiosis (http://www.ncbi.nlm.nih.gov/pubmed/25999229) Human babesiosis. (http://www.ncbi.nlm.nih.gov/pubmed/22716978)

A 66-Year-Old Man Comes to the Hospital Due to 2