68 years old female presents with an increase in airways' mucus production within last few days.
Patient has severe dyspnea at rest and exertion (can't speak almost at all), and has thick airways' mucus production.
Review of systems: She has severe cough, has history of fevers, and had no contact with others with signs or symptoms of infection.
Patient history revealed that patient has not been on dialysis, has not been living in a nursing home or other long-term care facility, and has not been hospitalized for more than 48 hours within the preceding 90 days. Additionally she has not been using any IV antibiotics within last 30 days.
Social history revealed that patient has 24 pack-years history of smoking, and has no risk for exposure to COVID-19 (SARS-CoV-2).
There is no relevant family history.
Physical examination: blood pressure 136/70 mmHg, heart rate of 70/min, temperature of 39.1 C (102.4 F), respiratory rate of 15/min, BMI of 19.44 kg/m2, and oxygen arterial saturation 98% on room air. Lungs' auscultation is positive for grossly asymmetric scattered inspiratory rales, mostly at the right base, is negative for decrease in breath sounds, is negative for wheezing, and is negative for rhonchi.
Serum procalcitonin (PCT) is 1.61 ng/ml (mcg/l). Blood white cells (WBC) is 19879 /ul. Chest x-ray shows no pleural effusion, and revealed no focal infiltrate.
What is the most probable diagnosis?