A 51-year-old man presents with a low grade fever, non productive cough and dyspnea for 2 weeks, which rapidly worsened over the last 2 days. He also felt unwell and experienced anorexia and weight loss over the preceding 3 months. He has engaged in unprotected sexual intercourse with commercial sex workers over the years, most recently last month. His chest x-ray shows diffuse interstitial infiltrates in the lung fields, with a normal cardiac silhouette.