About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- HIV-1 (most common worldwide) and HIV-2 (mainly West Africa). Transmitted via sexual contact (most common in UK), blood-borne, and vertical (mother-to-child)
- Seroconversion illness (2-6 weeks post-exposure): glandular fever-like illness (fever, rash, pharyngitis, lymphadenopathy) — often missed. HIGH viral load at this stage = highly infectious
- Diagnosis: 4th-generation HIV test (combined p24 antigen + HIV antibody) — window period ~4 weeks. Confirmatory test on second sample
- ART (antiretroviral therapy): start in ALL HIV-positive patients regardless of CD4 count (BHIVA). Standard regimen: 2 NRTIs + integrase inhibitor (e.g. tenofovir/emtricitabine + dolutegravir)
- U=U: undetectable viral load = untransmittable. PrEP (pre-exposure prophylaxis) with tenofovir/emtricitabine for high-risk individuals
Overview
Human immunodeficiency virus (HIV) is a retrovirus that infects CD4+ T-lymphocytes, macrophages, and dendritic cells. Without treatment, progressive CD4 depletion leads to acquired immunodeficiency syndrome (AIDS) — defined by CD4 <200 cells/µL or the presence of an AIDS-defining illness (e.g. Pneumocystis pneumonia, Kaposi sarcoma, CNS toxoplasmosis, CMV retinitis). Modern antiretroviral therapy (ART) is highly effective — patients who achieve an undetectable viral load have near-normal life expectancy and cannot transmit HIV sexually (U=U: undetectable = untransmittable).
Epidemiology
There are approximately 105,000 people living with HIV in the UK, of whom ~5% remain undiagnosed. The most common route of transmission in the UK is sexual (both MSM and heterosexual). New diagnoses have declined significantly since the introduction of PrEP and expanded testing. Late diagnosis (CD4 <350 at diagnosis) remains a problem and is associated with increased morbidity and mortality. NICE recommends routine HIV testing in high-prevalence areas (>2 per 1,000) and in patients presenting with HIV indicator conditions.
Clinical Features
Symptoms
Primary HIV infection (seroconversion, 2-6 weeks post-exposure): fever, malaise, pharyngitis, maculopapular rash, myalgia, mouth ulcers — resembles glandular fever
Chronic asymptomatic phase: may last years without treatment, gradual CD4 decline
Weight loss, chronic diarrhoea, recurrent infections as CD4 falls
Oral candidiasis, oral hairy leukoplakia (EBV — raised white patches on tongue lateral borders)
Recurrent herpes zoster (shingles) — especially in young adults
PCP: dry cough, progressive dyspnoea, hypoxia (CD4 <200)
Headache, confusion, seizures (CNS toxoplasmosis, cryptococcal meningitis, PML — CD4 <100)
Signs
Generalised lymphadenopathy
Oral candidiasis (thrush)
Seborrhoeic dermatitis (often florid)
Kaposi sarcoma: violaceous/purple skin plaques or nodules (HHV-8 associated)
Wasting syndrome (AIDS-defining)
Signs of opportunistic infections (see specific conditions)
Investigations
First-line
4th-generation HIV testCombined p24 antigen + HIV-1/2 antibody test. Detects infection from ~4 weeks post-exposure (window period). Positive result must be CONFIRMED on a second sample
Point-of-care HIV testRapid antibody test (finger-prick) — result in minutes. If reactive, must be confirmed with laboratory test
Second-line
CD4 countBaseline and serial monitoring. CD4 >500 = mild immunosuppression. CD4 200-500 = moderate. CD4 <200 = severe (AIDS), high risk of opportunistic infections
HIV viral load (RNA PCR)Quantifies circulating virus. Used to monitor ART response — aim for undetectable (<50 copies/mL). Also used for diagnosis in acute seroconversion when antibody test may be negative
HIV resistance genotypingBefore starting ART — identifies transmitted drug resistance mutations to guide regimen selection
Specialist
Baseline bloodsFBC, U&Es, LFTs, lipids, glucose, hepatitis B/C serology, syphilis serology, toxoplasma serology, CMV serology, VZV serology
HLA-B*5701Screen BEFORE prescribing abacavir — positive HLA-B*5701 = high risk of hypersensitivity reaction (do NOT prescribe abacavir)
CXR, cervical smear, STI screenBaseline investigations at diagnosis
1
Antiretroviral therapy (ART)
- Start ART in ALL patients regardless of CD4 count (BHIVA 2022) — early treatment improves outcomes and prevents transmission
- Standard first-line regimen: 2 NRTIs (tenofovir DF/emtricitabine or tenofovir AF/emtricitabine) + integrase inhibitor (dolutegravir or bictegravir)
- Monitor viral load at 4-8 weeks, then every 3-6 months. Target: undetectable viral load (<50 copies/mL)
- Adherence is critical — missed doses increase risk of resistance. Single-tablet regimens (STRs) improve adherence
- Drug interactions: check with Liverpool HIV Drug Interactions Checker (www.hiv-druginteractions.org)
2
Opportunistic infection prophylaxis
- CD4 <200: co-trimoxazole prophylaxis against PCP (Pneumocystis jirovecii pneumonia)
- CD4 <100: consider azithromycin prophylaxis against MAC (Mycobacterium avium complex)
- CD4 <50: regular fundoscopy for CMV retinitis screening
- Stop prophylaxis when CD4 recovers >200 for ≥3 months on ART
3
Prevention
- PrEP (pre-exposure prophylaxis): tenofovir DF/emtricitabine for HIV-negative individuals at high risk — available free on NHS since 2020
- PEP (post-exposure prophylaxis): 28-day course of ART within 72 hours of exposure (ideally within 24 hours)
- U=U: patients with sustained undetectable viral load (<200 copies/mL) cannot transmit HIV sexually — important for patient counselling and reducing stigma
- Condom use, harm reduction (needle exchange), antenatal screening
4
Vertical transmission prevention
- All pregnant women screened for HIV at booking (opt-out testing)
- ART during pregnancy: continue or start ART immediately — viral suppression is the key to prevention
- Planned caesarean section if viral load >50 copies/mL near delivery
- Neonatal ART prophylaxis for 2-4 weeks post-delivery
- Avoid breastfeeding in UK (where safe formula is available) — although women with undetectable VL may choose to breastfeed with appropriate support and monitoring
Complications
- AIDS-defining illnesses: PCP, Kaposi sarcoma, CNS toxoplasmosis, CNS lymphoma, cryptococcal meningitis, CMV retinitis, oesophageal candidiasis, TB, MAC, PML (JC virus)
- Immune reconstitution inflammatory syndrome (IRIS): Paradoxical worsening of symptoms after starting ART (immune system recovers and mounts inflammatory response to pre-existing infections)
- Cardiovascular disease: Increased risk — both from HIV-related chronic inflammation and some ART drugs (protease inhibitors → dyslipidaemia)
- HIV-associated neurocognitive disorder (HAND): Cognitive impairment despite viral suppression
- Non-AIDS malignancies: Increased risk of lung cancer, anal cancer, Hodgkin lymphoma
UKMLA Exam Tips
- 1Seroconversion illness looks like glandular fever — if Monospot/Paul-Bunnell is NEGATIVE, consider HIV testing
- 2CD4 <200 = PCP prophylaxis (co-trimoxazole). CD4 <100 = toxoplasmosis and MAC risk. CD4 <50 = CMV retinitis
- 3PCP: bilateral perihilar ground-glass opacities on CXR, desaturation on exertion, raised LDH. Diagnose with induced sputum or BAL for PCP immunofluorescence
- 4Cryptococcal meningitis: low CD4, headache, India ink stain of CSF (encapsulated yeast), raised CSF opening pressure. Serum/CSF cryptococcal antigen (CrAg)
- 5HLA-B*5701: MUST check before prescribing abacavir — hypersensitivity reaction
- 6U=U (Undetectable = Untransmittable) is a critical public health message and exam-relevant concept
- 7HIV indicator conditions (should prompt HIV testing): TB, lymphoma, severe/recurrent herpes zoster, oral candidiasis, unexplained lymphadenopathy, hepatitis B/C
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