Q. A 36-year-old woman presents to her primary care physician with a 4-day history of fever, headache, muscle aches, and a dry cough. She mentions that a few of her coworkers have been sick with similar symptoms recently. Her vital signs are as follows: temperature 38.9°C (102°F), heart rate 95 beats/min, respiratory rate 18 breaths/min, and blood pressure 115/75 mm Hg. On physical examination, she appears fatigued and has mild crackles in both lung fields. Which of the following is the most likely diagnosis?