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.
WBC/DC: 4,250/mm3 (4,600 - 11,000) 70% neutrophils 25% lymphocytes Hb: 12.6 g/dL (11.5 - 18.5) Platelets: 350,000/mm3 (150,00 - 450,000)
The HIV screening test is positive. A follow-up western blot assay is also positive.
On 60% oxygen: PaO2: 60.5 mmHg (> 62 on room air) PaCO2: 25.1 mmHg (35 - 45) pH: 7.53 (7.35 - 7.45) HCO3: 26 mmol/L (18 - 24)
Gram stain: negative Ziehl-Neelsen stain: negative Giemsa stain: multiple thick walled cysts and pleomorphic trophozoites with reddish nuclei and bluish cytoplasm Methenamine Silver stain: Stains the walls of the cysts