Pneumonia USMLE Step 1 Practice Question

A 32-year-old woman with HIV presents to the emergency department with a 2-week history of progressive dyspnea, fever, and nonproductive cough. She reports no antiretroviral therapy or prophylactic medication use. Vital signs: temperature 38.5°C, heart rate 108/min, respiratory rate 28/min, oxygen saturation 88% on room air. Physical examination reveals bilateral fine crackles on auscultation. Chest X-ray shows bilateral interstitial infiltrates with a ground-glass appearance. Laboratory studies reveal CD4+ count of 80/μL, lactate dehydrogenase 450 U/L, and negative sputum acid-fast bacilli smears. Which of the following is the most likely diagnosis?