Review Question - QID 212538

A 3-year-old girl is brought to the pediatrician by her father for fever and cough. The patient’s father states that she had a sore throat and runny nose 2 weeks ago. Then last night she developed a productive cough and a fever. The father is worried that this is pneumonia again, and reports that she has been hospitalized 5 times already with pneumonia. Her medical history is also significant for chronic diarrhea. The father reports that the patient has 2 older brothers who are both healthy. The patient’s temperature is 102°F (38.9°C), blood pressure is 102/60 mmHg, pulse is 110/min, and respirations are 28/min with an oxygen saturation of 94% on room air. On physical examination, decreased breath sounds are appreciated on the right. A chest radiography shows consolidation in the right upper lobe, consistent with pneumonia. An antibody panel and flow cytometry are obtained in the setting of the patient’s recurrent infections. The results show a normal lymphocyte count with low levels of IgA, IgG, and IgE and elevated levels of IgM. Which of the following is the patient most at risk for developing?