Patient: 10-month-old male Presenting Complaint: Recurrent ear and respiratory infections over the past 4 months History of Present Illness: The child’s mother reports recurrent ear infections, sinus infections, and two episodes of bronchitis since the age of 6 months. The infections typically resolve with antibiotics, but they seem to recur every 3 to 4 weeks. He has not had any severe infections, hospitalizations, or weight loss. His appetite is good, and he is meeting developmental milestones. The mother denies any history of diarrhea, skin abscesses, or opportunistic infections. The child has no known allergies and is up to date on vaccinations. He recently had a mild cold with runny nose and cough, which resolved without complications. Past Medical History: • Full-term birth, no complications • No significant illnesses before 6 months of age Family History: • No family history of primary immunodeficiencies or recurrent infections Physical Examination: • Vital signs: Normal • Growth and development: Normal for age (weight and height in the 50th percentile) • ENT: Mild erythema of the right tympanic membrane (acute otitis media) • Chest: Clear to auscultation • Skin: No rashes or lesions Laboratory Investigations: • Serum IgG: Low for age (below the 10th percentile) • Serum IgA and IgM: Normal • B-cell and T-cell counts: Normal • Vaccine response: Adequate response to tetanus and pneumococcal vaccines • Complete blood count: Normal with no signs of neutropenia What is the most likely diagnosis?
