An HIV-positive patient with a CD4 count of 120 cells per microlitre has progressive dyspnoea and diffuse bilateral interstitial infiltrates. Bronchoalveolar lavage stained with Grocott methenamine silver shows clusters of cup-shaped cysts, 5 to 8 micrometres, with a collapsed crescentic appearance. Which statement about this organism is correct?

• A It can be readily cultured on Sabouraud dextrose agar
• B Giemsa stain demonstrates the characteristic cyst wall
• C The cyst wall contains ergosterol, making it susceptible to amphotericin B
• D Prophylaxis with co-trimoxazole is indicated below a CD4 count of 200 cells per microlitre ✓

Explanation

Pneumocystis jirovecii pneumonia is prevented with co-trimoxazole once the CD4 count falls below 200 cells per microlitre, one of the best-established prophylaxis thresholds in medicine. The organism cannot be cultured routinely, ruling out A. Its cell membrane lacks ergosterol, so amphotericin D and standard azoles are ineffective, ruling out C. Methenamine silver stains the cyst wall, whereas Giemsa demonstrates the trophic forms, ruling out B.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.