Pneumonia

A 66 year-old woman comes to the emergency department because of worsening confusion for the past day. Past medical history is significant for Parkinson disease and diabetes mellitus type 2. She is admitted for observation and returns to baseline mentation after 3 days, but on the third day she begins complaining of worsening shortness of breath and cough productive of white sputum. The cough is also associated with chest pain during deep inhalation. Associated symptoms include sinus congestion and headache.  Her temperature is 38.3°C (101.3°F), pulse is 92/min, respirations are 22/min, blood pressure is 140/90 mm Hg, and oxygen saturation is 94% on 2L O2 via nasal cannula. Labs and imaging are pending. At this time, which of the following is the most likely diagnosis?