A 33-year-old man has an acute respiratory distress. Over the last 3 days, he noted feeling short of breath with exertion and dry cough. His temp is 39.1 "C, BP is 110/72 mmHg, HR is 98/min,RR is 22/min and SPO2 is 89% on room air. Chest exam reveals diffuse crepitation bilateral. His chest radiograph revealed bilateral lung infiltrate. What is the single most likely diagnosis?