Clinical microbiological case: facial inflammation in a child with a subnormal serum concentration of IgG2.

A 16-month-old boy presented with a history of facial pain and swelling during the last 3 days and temperature elevation up to 39 °C. He had been given oral cefuroxime axetil therapy (30 mg/kg/24 h) for the preceding 72 h, but the inflammation did not improve. The child was previously healthy and his growth was normal. The physical examination revealed tenderness, erythema, slight swelling and heat over an area with clearly demarcated edges, extending from the upper lip to the skin left of the nose, without purulent collection. A small abscess was found on the base of the left nasal cavity. Lymph nodes were not palpable. The child was in good clinical condition, with a temperature of 38.4 °C and a pulse of 120/min. The initial laboratory investigation showed a white blood cell (WBC) count of 13 800/μL with 40% neutrophils, hemoglobin 13.6 g/dL, hematocrit 38%, erythrocyte sedimentation rate (ESR) 55 mm/h and C-reactive protein level (CRP) 56 mg/L. Radiographic examination of the paranasal sinuses was normal. Aerobic and anaerobic cultures from the anterior nares, as well as blood and urine cultures, were taken. The initial therapy was changed to cefuroxime sodium administered intravenously (150 mg/kg/24 h). From the second hospitalization day, the child was afebrile and his clinical condition had clearly improved. Aerobic blood cultures became positive in the automated BacT/Alert-System (Organon Technica Durham, NC, USA), and immediate Gram staining showed a typical Gram-negative rod. Subcultures on blood, chocolate and MacConkey agar plates were made to isolate the organism (Figure 1). Urine cultures yielded significant growth of a Gram-negative oxidase-positive rod (>105/mL), with dry, wrinkled, light brown pigmented colonies. Nasal cultures yielded a similar organism in combination with Staphylococcus aureus. A basic immunologic screening was ordered. The immunoglobulin levels were in the normal ranges for the child's age, except for subnormal serum concentrations of members of the IgG2 subclass (IgM 88.7 mg/dL, IgA 32.4 mg/dL, IgG 503 mg/dL, IgG1 479 mg/dL, IgG2 5 mg/dL, IgG3 24 mg/dL and IgG4 16 mg/dL). Lymphocyte subpopulation counts, chemotaxis of polymorphonuclear cells and nitroblue-tetrazolin reduction test were also normal. 1What is your clinical diagnosis? Was the decision to take blood and urine cultures justified on admission?2What are the most common etiologic agents of this syndrome?3What would be your therapeutic approach in similar cases? What would be your therapeutic approach in this patient?4Would you order an immunologic screening in the above case?