A nurse on the pediatric unit is assessing an infant who is 2 months old. The infant was born by spontaneous vaginal delivery at 39 2/7 weeks, Apgar 8 and 9, received regular newborn care and screening, and was discharged home with the mother. The infant weighed 2.04 kg (4 lbs 8 oz) and was 18 inches (45.7 cm) in length at birth. The guardians report that in the last 3 days, the infant has been fussy and hard to console within the first hour after feeding. The infant takes formula and vomits after each feeding, about 60-90 mL (2 to 3 ounces) of partially digested formula. Which of the following conditions is the infant most likely to have?

The correct answer is A: Pyloric stenosis. Pyloric stenosis is a condition where there is a narrowing of the opening between the stomach and the small intestine (pylorus), leading to projectile vomiting after feeding. In this case, the infant's symptoms of vomiting after feeding, especially projectile vomiting, suggest pyloric stenosis. The age of onset (typically around 2-8 weeks old), the pattern of vomiting, and the difficulty in consoling after feeding are classic signs of pyloric stenosis. The other choices (B: Gastroesophageal reflux, C: Celiac disease, D: Lactose intolerance) do not fully align with the infant's symptoms and history provided, making them less likely diagnoses. Gastroesophageal reflux may present with spitting up but not typically with projectile vomiting. Celiac disease and lactose intolerance are less likely given the infant's age and clinical presentation.