A 3-year-old boy is brought to his pediatrician’s office because of prolonged ear pulling and discomfort. The condition started a week ago, and his parents are concerned that he has developed another ear infection. He has had multiple minor respiratory tract infections with productive cough and ear infections over the last year; he has also been hospitalized once with community-acquired pneumonia. During his last ear infection, there was some discussion of myringotomy. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. Today, the vital signs include: temperature 39.0°C (102.0°F), blood pressure 100/65 mm Hg, heart rate 110/min, and respiratory rate 30/min. His left ear is tender and appears red and irritated. Examination with an otoscope reveals a swollen canal and a bulging tympanic membrane. A review of previous medical records reveals the following chest X-ray taken 2 months ago. What is the underlying cause of his recurrent infections?