Review Question - QID 106734

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Encapsulated Bacteria Overview QID: 106734 (M1.MC.15.75)

QID 106734 (Type "106734" in App Search)

A 23-year-old male is involved in a motorcycle accident and is brought to the nearest level 1 trauma center. On arrival, the patient's vitals are T: 37 deg C, HR: 102 bpm, BP: 105/60, RR: 12, SaO2: 100%. A FAST exam is performed during the initial workup which demonstrates significant free fluid in the abdomen (Figure A). An abdominal CT scan is subsequently obtained which demonstrates a grade V splenic laceration (Figure B) and the patient is emergently brought to the operating room where a splenectomy is successfully performed. Following surgery, this patient will be at increased risk of infection with which of the following organisms?

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Legionella

30/548

Listeria

23%

125/548

Shigella dysenteriae

42/548

K. pneumoniae

61%

335/548

Chlamydia

7/548

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Asplenic patients are at increased risk of infection with encapsulated organisms such as K. pneumoniae.

Encapsulated bacteria have capsules which serve as an antiphagocytic virulence factor. These bacteria include S. pneumoniae, H. influenzae type B, N. meningitidis, E. coli, Salmonella, K. pneumoniae, group B Strep, and B. fragilis. The immune system combats these organisms by opsonizing and then clearing them by the spleen. Thus, asplenic patients have decreased ability to opsonize organisms and are at increased risk of infection with encapsulated bacteria. Asplenic patients are recommended to have the S. pneumoniae, H. influenzae, and N. meningitidis vaccines to prevent such infection. It is recommended that these vaccines be given 14 days post-splenectomy in non-elective cases.

Brigden reviews the detection, education, and management of the asplenic or hyposplenic patient. She states fulminant, potentially life-threatening infection is a major long-term risk after splenectomy or in persons who are functionally hyposplenic as a result of various systemic conditions. Most of these infections are caused by encapsulated organisms such as pneumococci, H. influenzae and meningococci. Management of patients with these conditions includes a combination of immunization, antibiotic prophylaxis, and patient education.

Saraceni and Schwed-Lustgarten present a case of pneumococcal sepsis-induced purpura fulminans in an asplenic adult patient. They state acute perturbations in the hemostatic balance of anticoagulation and procoagulation precede the manifestation of purpura fulminans, a rare syndrome of intravascular thrombosis and hemorrhagic infarction of the skin. Hallmarks include small vessel thrombosis, tissue necrosis, and disseminated intravascular thrombosis. Early intravenous antibiotic administration and hemodynamic support are cornerstones in management.

Figure A demonstrates a positive FAST exam ultrasound showing free fluid in Morrison's pouch. Figure B is a CT scan demonstrating a severe grade V splenic laceration.

Incorrect Answers:
Answers 1-3,5: These organisms are NOT encapsulated organisms, and thus asplenic patients are not at increased risk of infection with these organisms.