Synopsis
Use CD4 count and organ syndrome to identify HIV-related opportunistic infection, obtain decisive samples, start time-critical therapy and sequence ART to avoid preventable immune-reconstitution harm.
- CD4 count predicts probability: PCP rises below 200, toxoplasma and cryptococcus below about 100, and CMV or disseminated MAC below about 50 cells/µL.
- Never use CD4 threshold alone; tuberculosis, bacterial infection and some malignancies occur at any count.
- PCP usually causes subacute dry cough, fever, exertional dyspnoea and diffuse ground-glass change with marked hypoxia.
Key red flags
Resting or exertional hypoxia with dry cough and bilateral interstitial change suggests PCP and needs urgent arterial blood gas.
Weeks of dry cough, fever, progressive exertional dyspnoea, tachypnoea and disproportionate hypoxia occurs commonly below CD4 200.
Investigation priorities
Map immune risk, baseline HIV activity and prophylaxis or ART urgency.
Management branches
Subacute respiratory illness, compatible imaging and immune deficiency produce hypoxia.
- Use ABCDE, obtain arterial gas, chest imaging, LDH and beta-D-glucan and send induced sputum or bronchoalveolar samples.
- Start high-dose co-trimoxazole immediately when probability is high, adjusting for weight, renal function and severe allergy.
Key medicines
Co-trimoxazole for PCP treatmentGive trimethoprim 15 to 20 mg/kg/day with sulfamethoxazole 75 to 100 mg/kg/day orally or intravenously in three or four divided doses for 21 days.
Prednisolone for moderate or severe PCPGive 40 mg orally twice daily on days 1 to 5, 40 mg once daily on days 6 to 10, then 20 mg once daily on days 11 to 21.