Pneumonia USMLE Step 1 Practice Question

A 34-year-old man with HIV infection presents to the emergency department with a 3-week history of progressive dyspnea and nonproductive cough. He reports subjective fever and night sweats. He was diagnosed with HIV 6 months ago but has not yet initiated antiretroviral therapy. Physical examination reveals tachypnea (respiratory rate 28/min) and oxygen saturation of 89% on room air. Temperature is 38.2°C. Chest X-ray shows bilateral symmetric ground-glass opacities predominantly in the perihilar and mid-lung zones. Laboratory studies reveal CD4+ count of 75 cells/mm³, HIV RNA >100,000 copies/mL, and serum LDH of 520 U/L (normal <400). Induced sputum Gram stain and routine bacterial culture are negative. Sputum AFB smear is negative. Which of the following is the most likely diagnosis?