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HIV
Everyone with HIV starts antiretroviral therapy at once, whatever the CD4 count, on an integrase-inhibitor-based regimen; below 200 CD4 cells TMP-SMX is added to prevent PCP, and an undetectable viral load means no sexual transmission.
Why it matters in the exam
Questions present HIV in several ways: a mononucleosis-like illness a few weeks after exposure (acute HIV, when antibodies may still be negative, so the viral load is tested), or a first opportunistic infection — Pneumocystis pneumonia with breathlessness, hypoxaemia and a high LDH, oesophageal candidiasis, cerebral toxoplasmosis or Cryptococcus. The first test is a fourth-generation assay (antigen and antibody together), followed by a confirmatory test. Treatment starts as early as possible, even on the day of diagnosis, with a regimen such as bictegravir/TAF/FTC or dolutegravir with two NRTIs.
Some exceptions and timings are tested: in cryptococcal meningitis antiretroviral therapy is delayed by 4–6 weeks, and with tuberculosis it is started within 2 weeks when CD4 is below 50 and within 8 weeks in others. HLA-B*57:01 is checked before abacavir. Prevention: CD4 below 200 → TMP-SMX against PCP (which also covers toxoplasmosis below 100 in IgG-positive people). In PCP with PaO2 below 70 mmHg, prednisone is added. PEP is given within 72 hours of exposure for 28 days, and PrEP (tenofovir/emtricitabine) is offered to people at high risk.
Key points
- Diagnosis: fourth-generation test; in acute HIV — viral load.
- Treatment for all, at once, on an integrase-inhibitor-based regimen.
- CD4 below 200 → TMP-SMX.
- Tuberculosis: ART within 2 weeks if CD4 below 50; Cryptococcus: delay 4–6 weeks.
- PEP within 72 hours for 28 days; PrEP at high risk.
Summary table
| Topic | Criterion | Action | Exam note |
|---|---|---|---|
| Diagnosis | Fourth-generation test (antigen + antibody) | Confirmatory test and viral load | In acute HIV antibodies may be negative |
| Starting treatment | Everyone with HIV, whatever the CD4 | Bictegravir/TAF/FTC or dolutegravir + 2 NRTIs | As early as possible, even the same day |
| PCP prevention | CD4 below 200 | TMP-SMX | Also covers toxoplasmosis when CD4 is below 100 |
| Timing with infections | Tuberculosis; Cryptococcus | TB: within 2 weeks if CD4 below 50, otherwise within 8; Cryptococcus: delay 4–6 weeks | Risk of IRIS |
| PCP | Hypoxaemia, high LDH, bilateral infiltrate | TMP-SMX; prednisone if PaO2 below 70 mmHg | Also pneumothorax |
| Exposure | PEP within 72 hours | 3 drugs for 28 days | PrEP for prevention at high risk |
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Sources
- DHHS Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents with HIV, 2024 — When to start, initial regimens and opportunistic infection prophylaxis
- EACS Guidelines, 2023 — Diagnosis, initial treatment, PEP and PrEP
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Human Immunodeficiency Virus Disease: AIDS and Related Disorders
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.