Review Question - QID 215035

A 26-year-old G1P1 woman with no prenatal care gives birth to a boy at 38 weeks' gestation via spontaneous vaginal delivery. The birth is unremarkable. According to the mother, she developed a mild flu-like illness 4 months ago but otherwise had an uncomplicated pregnancy. She does not know if she received her childhood vaccinations. The newborn’s weight is 6 lb and 5 oz, length is in the 45th percentile, and head circumference is in the 99th percentile. His temperature is 97.8°F (36.6°C), blood pressure is 66/42 mmHg, pulse is 146/min, and respirations are 45/min. On physical exam, the infant has a bulging anterior fontanelle. The fundoscopic examination is notable for posterior segment inflammation bilaterally. The skin is pink, without cyanosis, jaundice, or any rash, and the cardiothoracic exam is benign. Head CT shows intracranial calcifications and ventriculomegaly. Subsequent serologic testing confirms the diagnosis. Which of the following is the most likely causative organism?