Opportunistic infection in HIV — Rapid

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.
Serum cryptococcal antigen and lumbar puncture with opening pressure are central in headache with advanced HIV.
Multiple basal-ganglia ring-enhancing lesions with positive toxoplasma IgG support cerebral toxoplasmosis, but lymphoma remains a key alternative.
CMV retinitis is a clinical ophthalmic emergency diagnosed by dilated retinal examination, not by blood PCR alone.
Start ART early during most opportunistic infections, but delay after cryptococcal meningitis and use a specialist timing plan for TB meningitis.
Begin co-trimoxazole PCP prophylaxis at the current CD4 or clinical threshold and stop only after sustained immune recovery on ART.

Key red flags

Resting or exertional hypoxia with dry cough and bilateral interstitial change suggests PCP and needs urgent arterial blood gas.

Headache, confusion or cranial neuropathy with CD4 below 100 cells/µL requires cryptococcal antigen and pressure-aware lumbar puncture.

Visual floaters, scotoma or acuity loss at CD4 below 50 cells/µL needs same-day dilated retinal examination for CMV.

Focal neurology, seizure or ring-enhancing lesions suggest cerebral toxoplasmosis, lymphoma, TB or fungal disease.

Clinical deterioration after ART may be immune-reconstitution inflammation, but treatment failure, resistance and a new infection must be excluded.

Cryptococcal or TB meningitis requires specialist delay of ART because early immune recovery can worsen intracranial inflammation.

Pneumocystis pneumonia

Weeks of dry cough, fever, progressive exertional dyspnoea, tachypnoea and disproportionate hypoxia occurs commonly below CD4 200.

Cryptococcal meningitis

Subacute headache, fever, cognitive change, cranial neuropathy or visual symptoms may occur with little meningism below CD4 100.

Cerebral toxoplasmosis

Headache, fever, seizures and focal deficits with multiple ring-enhancing brain lesions usually occurs below CD4 100.

CMV retinitis

Investigation priorities

CD4 count and HIV viral loadFirst step

Map immune risk, baseline HIV activity and prophylaxis or ART urgency.

Management branches

LUNGTreat suspected PCP promptly

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.
Add corticosteroids within 72 hours when PaO2 is below 9.3 kPa or the alveolar–arterial gradient exceeds 4.7 kPa.
Treat for 21 days and start ART within about two weeks when clinically stable and no competing CNS infection changes timing.

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.Use the trimethoprim component for dosing, adjust renal function and monitor rash, marrow, potassium, creatinine and liver; seek specialist alternatives for severe allergy.

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.Start within 72 hours of PCP therapy, exclude competing steroid-harmed infection as far as possible and monitor glucose, mood and secondary infection.

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