A previously well, 56-day-old female infant arrives at your office with a 1-day history of fever (up to 38.9°C). The parents deny cough, congestion, nausea, rash, skin lesions, vomiting, and diarrhea. No one else at home is ill. The baby is taking 2oz of formula instead of 3oz every 2 to 3 hours.
Her birth was a full-term, uncomplicated pregnancy and delivery; her nursery stay was without complications; and she went home in 2 days. She has no prior illnesses. She received hepatitis B vaccine in nursery. The family has been in your practice since the birth of the oldest child and has kept appointments reliably.
Vital signs: 38.8°C, HR 130 beats/min, and RR 24 breaths/min. Physical examination shows a strong cry, but she is consolable by her mother. She is comfortable in her mother’s arms and well appearing and is otherwise unremarkable.
Laboratory results show the following:
White blood cell count, 12,800/µL (12.8 × 109/L), with 45% neutrophils, 3% bands; 49% lymphocytes; 3% monocytes
Hemoglobin, 13.4 g/dL (134 g/L)
Platelet count, 227 × 103/µL (227× 109/L)
A urinalysis shows the following:
Specific gravity, 1.017
pH, 7.0
Dipstick, negative
The blood and urine cultures are pending.
Of the following, the BEST next step in the management of this infant’s condition would be to
