A 15-year-old boy is evaluated for fever, headache, malaise, and cough 3 weeks after returning from summer camp. Lung auscultation is unremarkable. Chest x-ray reveals nodular infiltrates. The patient's blood samples are collected for analysis in anticoagulated tubes, which are transported submerged in ice; when taken out several minutes later, turbidity and clumping are noted. Warming the tube to body temperature leads to rapid dissolution of the clumps. Which of the following organisms is most likely responsible for this patient's condition?

Question

A 15-year-old boy is evaluated for fever, headache, malaise, and cough 3 weeks after returning from summer camp.  Lung auscultation is unremarkable.  Chest x-ray reveals nodular infiltrates.  The patient's blood samples are collected for analysis in anticoagulated tubes, which are transported submerged in ice; when taken out several minutes later, turbidity and clumping are noted.  Warming the tube to body temperature leads to rapid dissolution of the clumps.  Which of the following organisms is most likely responsible for this patient's condition?

Quizplus · Accepted Answer

Mycoplasma pneumoniae infection is common in adolescents and usually presents with tracheobronchitis or walking pneumonia. The pathogen attaches to the respiratory epithelium using surface antigens (I-antigen) that are also present on the plasma membrane of erythrocytes. Therefore, patients with M pneumoniae typically develop cross-reactive IgM antibodies that can attach to red blood cells, activate the complement system, and cause erythrocyte lysis. These cross-reacting antibodies are called cold agglutinins because they bind to erythrocytes most strongly at temperatures below core body temperature. Testing for cold agglutinins can be done at the bedside by drawing blood into an edetate disodium-containing tube and placing it in a cup of ice. Removing the tube after several seconds will reveal clumping/agglutination that resolves as the tube warms. Cold agglutinins are often asymptomatic, but some patients develop mild intravascular hemolytic anemia that usually resolves after 6-8 weeks (when IgM antibody titers fall). Patients who have infectious mononucleosis and certain hematologic malignancies also commonly develop cold agglutinins. Educational objective: Infection with Mycoplasma pneumoniae can result in the formation of cold agglutinins, which are IgM antibodies (primarily) that bind red blood cells and cause clumping/agglutinations at low body temperatures. Other illnesses resulting in cold agglutinin formation include infectious mononucleosis and certain hematologic malignancies.

A 15-Year-Old Boy Is Evaluated for Fever, Headache, Malaise, and Cough