1. David S. Kim, MD* 2. Abiara V. Agwu, MD* 3. Carol J. Baker, MD* 1. *Department of Pediatrics, McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth), Houston, TX An 8-week-old male infant presents to the emergency department with 5 days of constipation and recent onset of fussiness, decreased feeding, and a swelling in the right neck. No temperature abnormalities are reported. The medical history is significant for preterm birth at 30 5/7 weeks’ gestation (weight, 930 g) via cesarean delivery due to preeclampsia and partial placental abruption to a 33-year-old mother with an unknown group B Streptococcus (GBS) status. During his neonatal admission he received antibiotics for 48 hours after delivery for a sepsis evaluation and topical ciprofloxacin, which resolved an episode of undefined otorrhea. After an otherwise uneventful hospital course, he was discharged at age 6 weeks. On examination in the emergency department, the vital signs are as follows: temperature, 97°F (36.1°C); heart rate, 172 beats/min; respirations, 40 breaths/min; blood pressure, 94/58 mm Hg; oxygen saturation, 100%; and weight, 2,400 g. The infant is in mild distress. An approximately 1-cm tender mass is palpable in the right submandibular region without overlying erythema. The remainder of the physical examination findings are normal. He has a total leukocyte count of 10,100/µL (10.1×109/L) with 20% bands. The basic metabolic panel and urinalysis findings are normal. Ultrasonography of the neck demonstrates symmetrical enlargement of numerous lymph nodes bilaterally, measuring up to 7 mm in the short axis, and without a drainable fluid collection (Fig). An abdominal radiograph is normal. Fig. Ultrasonography of the neck performed at presentation highlighting two of the numerous enlarged lymph nodes that were present bilaterally. The size and number of lymph nodes were increased for age. A fluid bolus improves the heart rate and capillary refill. A single dose of clindamycin is administered for a presumptive diagnosis of bacterial lymphadenitis. Because the infant now appears well, clindamycin is discontinued. Sixteen hours later, the infant has increasing …