Review Question - QID 214552

A 6-month-old girl is brought to the clinic for general malaise and fatigue. Her mother states that over the past month the patient has had “low energy.” She is eating less compared to before and stops feeding after 5 minutes. The patient was born at 38 weeks of gestation with no complications. She has followed her growth curves and her developmental milestones without issues. She is up to date on her vaccines, and her mother denies any smoking in the household. The mother denies any emesis, diarrhea, cough, fevers, or sick contacts; however, she is a teacher and a student of hers was recently sick with fever and a rash. Physical examination demonstrates a well-nourished infant with conjunctival pallor and the findings shown in Figure A. Laboratory studies are shown below:

Leukocyte count: 7,500/mm^3 with normal differential
Hemoglobin: 4.2 g/dL
Platelet count: 190,000/mm^3
Mean corpuscular hemoglobin concentration: 32%
Mean corpuscular volume: 104 µm^3
Reticulocyte count: 1%
Lactate dehydrogenase: 130 U/L

What is the most likely explanation for this patient’s findings?