Q. A 17-year-old high school student presents to the clinic with a 1-week history of a persistent dry cough, malaise, and low-grade fever. The patient reports that several classmates have experienced similar symptoms. Her vital signs are: temperature 99.7°F (37.6°C), blood pressure 110/70 mmHg, heart rate 85 bpm, respiratory rate 18 breaths/min, and oxygen saturation 98% on room air. Physical examination reveals bilateral scattered crackles on lung auscultation, and no other significant findings. A chest X-ray shows patchy interstitial infiltrates. Based on the clinical presentation, what is the most likely causative agent of this patient's pneumonia?