HIV and AIDS — Causes, Stages, Diagnosis & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Human Immunodeficiency Virus (HIV) is a lentivirus that primarily infects CD4+ T-lymphocytes (T-helper cells), macrophages, and dendritic cells — progressively depleting cellular immunity. Without treatment, untreated HIV infection leads to Acquired Immunodeficiency Syndrome (AIDS) — defined as a CD4 count below 200 cells/mcL or the occurrence of an AIDS-defining illness — typically within 10 years of infection. Globally, 39 million people live with HIV (UNAIDS 2023). With modern antiretroviral therapy (ART), HIV is now a manageable chronic condition — people who start ART early can expect near-normal life expectancy and quality of life. The concept U=U (Undetectable = Untransmittable) — endorsed by all major HIV organisations — demonstrates that people with an undetectable viral load on ART cannot sexually transmit HIV. In the UK, approximately 106,000 people live with HIV; approximately 5,000 new diagnoses occur annually. Key challenges remain: late diagnosis (30% are diagnosed late in the UK — CD4 below 350 — missing the opportunity for early treatment); stigma; and global inequity in ART access.

HIV is caused by two types: HIV-1 (responsible for the global pandemic — highly diverse, multiple subtypes) and HIV-2 (predominantly in West Africa — slower progression, lower transmissibility). Transmission requires direct contact with infected blood, breast milk, semen, pre-seminal fluid, rectal fluid, vaginal fluid, or CSF. Routes of transmission: sexual transmission (most common globally — anal sex carries highest per-act risk: 138 per 10,000 exposures for receptive anal intercourse; vaginal sex: 8-11 per 10,000 for receptive vaginal intercourse; risk is bidirectional — insertive partners also at risk); parenteral (sharing needles/injecting equipment — 63 per 10,000 exposures; contaminated blood products — now rare with screening); vertical/mother-to-child transmission (MTCT — during pregnancy, labour, delivery, or breastfeeding — risk below 1% with ART and formula feeding, compared to 25-40% without intervention). Risk factors for transmission: high plasma viral load of the HIV-positive partner (primary infection or untreated HIV have the highest viral load — most contagious); presence of STIs (particularly ulcerative STIs — herpes, syphilis — increase HIV susceptibility and infectivity); sexual network; injection drug use; uncircumcised male (circumcision reduces HIV risk by 60% in male heterosexual insertive sex). HIV is NOT transmitted by: casual contact, saliva, tears, sweat, sharing cutlery, toilet seats, hugging, or insect bites.

HIV infection progresses through three clinical stages: Stage 1 — Acute HIV infection (primary HIV): occurs 2-4 weeks after exposure; 50-80% experience a flu-like illness — seroconversion illness or acute retroviral syndrome (ARS): fever, lymphadenopathy, sore throat, rash (maculopapular, truncal), myalgia, arthralgia, diarrhoea, headache, and malaise; typically lasts 2-4 weeks; frequently misdiagnosed as influenza or glandular fever; viral load is extremely high (1 million+ copies/mL) — most infectious period; HIV-specific antibodies develop (seroconversion) 2-8 weeks post-exposure. Stage 2 — Chronic HIV infection (clinical latency): asymptomatic phase — CD4 count gradually declines (average 50-100 cells/mcL/year); typically lasts 8-10 years without treatment (shorter in late infection, older age, co-infections); may have persistent generalised lymphadenopathy (PGL); HIV replication continues despite lack of symptoms. Stage 3 — AIDS (Acquired Immunodeficiency Syndrome): CD4 count below 200 cells/mcL or AIDS-defining conditions; AIDS-defining illnesses: Pneumocystis jirovecii pneumonia (PCP — the most common AIDS-defining illness — CD4 typically below 200; presents with progressive breathlessness, dry cough, fever, bilateral interstitial shadowing); CMV retinitis (CD4 below 50 — visual loss); toxoplasma encephalitis (CD4 below 100 — ring-enhancing lesions on CT/MRI); oesophageal candidiasis; cryptococcal meningitis; MAC (Mycobacterium avium complex — disseminated infection); HIV encephalopathy and AIDS dementia complex; Kaposi's sarcoma (HHV-8 associated — skin and visceral lesions); invasive cervical cancer; extrapulmonary TB. With modern ART, AIDS is now rare in high-income countries in treated patients.

HIV testing: recommended annually for all sexually active adults in high-prevalence areas; at every sexual health screen for MSM, PWID, and people from high-prevalence countries. HIV antibody/antigen (Ag/Ab) combination (4th generation) ELISA test: detects both p24 antigen and HIV antibodies; window period of 45 days from exposure (detects 99%+ of infections by 45 days; 95%+ by 28 days); point-of-care (rapid) tests available (INSTI, BioSure — sensitivity above 99%; 45-day window period). HIV RNA PCR (viral load): detects HIV RNA directly — useful in acute HIV (before antibody development); not used for primary diagnosis routinely; confirms acute HIV when antibody test borderline or early infection suspected. Confirmatory testing: all reactive screening tests confirmed by Western blot or additional assay. Post-HIV diagnosis monitoring: CD4 count (cells/mcL) — primary measure of immunological status and treatment urgency; CD4 below 350 — start ART urgently; CD4 below 200 — AIDS-defining; HIV viral load (copies/mL) — measure of viral replication; below 50 copies/mL = undetectable; baseline resistance testing (genotype) — identifies transmitted drug resistance; FBC, U&E, LFTs, lipids, glucose, HbA1c (metabolic monitoring for ART side effects); HLA-B*5701 testing (before abacavir — hypersensitivity reaction testing); STI screen (syphilis, gonorrhoea, chlamydia, hepatitis B, hepatitis C); TB screen (IGRA, CXR). CD4 monitoring while on ART: every 3-6 months until stable; viral load every 3-6 months initially, every 6-12 months if stable and undetectable.

Antiretroviral therapy (ART) — all people with HIV should start ART regardless of CD4 count (BHIVA and WHO guidelines — 2024): modern ART achieves viral suppression (undetectable viral load below 50 copies/mL) in 97%+ of patients with good adherence; effective ART prevents AIDS, AIDS-defining infections, and transmission. Preferred first-line regimens (WHO and BHIVA guidelines, 2024): dolutegravir (DTG) 50 mg + tenofovir disoproxil fumarate (TDF) 300 mg + lamivudine (3TC) 300 mg once daily (generic available — affordable globally); or bictegravir (BIC) 50 mg + emtricitabine (FTC) 200 mg + tenofovir alafenamide (TAF) 25 mg once daily (Biktarvy — higher barrier to resistance; preferred in UK NHS — NICE recommended). Integrase strand transfer inhibitors (INSTI) — dolutegravir, bictegravir, cabotegravir — are the backbone of modern ART (high efficacy, excellent tolerability, high resistance barrier). Long-acting injectable ART: cabotegravir (CAB) 600 mg + rilpivirine (RPV) 900 mg IM injection every 2 months (Cabenuva) — for virologically stable patients; eliminates daily pill-taking; NICE approved 2023; highly effective alternative for those with adherence challenges or who prefer injections. Opportunistic infection (OI) prophylaxis: CD4 below 200 — co-trimoxazole (trimethoprim-sulfamethoxazole) 960 mg daily for PCP prophylaxis; CD4 below 50 — azithromycin weekly for MAC prophylaxis; fluconazole for cryptococcal disease prevention. PrEP (pre-exposure prophylaxis): TDF/FTC (Truvada or generic) once daily or on-demand (2-1-1 method) — reduces HIV acquisition risk by 99% in people at high risk of HIV; available on NHS since 2020; strongly recommended for MSM with multiple partners, HIV-negative partners of HIV-positive people not on ART, PWID. nPEP (non-occupational post-exposure prophylaxis): TDF + FTC + raltegravir or dolutegravir — started within 72 hours of exposure (ideally within 4 hours), taken for 28 days — reduces transmission risk by approximately 80%. Treatment monitoring: viral load 4 weeks after starting ART (confirm suppression); every 3-6 months until stable (below 50 copies/mL); drug resistance testing if viral load above 200 copies/mL on ART.

Without effective ART, HIV causes progressive immunodeficiency and eventually AIDS with life-threatening opportunistic infections and malignancies. AIDS-defining illnesses (CD4 below 200 cells/mcL): Pneumocystis jirovecii pneumonia (PCP — the most common AIDS-defining illness in high-income countries; causes progressive hypoxic respiratory failure); cerebral toxoplasmosis (ring-enhancing lesions on MRI causing seizures and focal neurological deficits); cryptococcal meningitis (the most common cause of adult bacterial meningitis in sub-Saharan Africa — causes headache, confusion, and papilloedema; treated with IV amphotericin B); CMV retinitis causing blindness; oesophageal candidiasis causing severe dysphagia; Mycobacterium avium complex (MAC) causing disseminated infection with fever, weight loss, and night sweats; Kaposi's sarcoma (HHV-8 — purple mucocutaneous and visceral lesions); primary CNS lymphoma; progressive multifocal leukoencephalopathy (PML — JC virus causing rapidly progressive dementia and focal deficits). Non-AIDS-defining complications (driven by chronic HIV-related inflammation): cardiovascular disease — approximately 2-fold increased MI risk even on ART; HIV-associated neurocognitive disorders (HAND — mild cognitive impairment in approximately 30–50% of people with HIV); HIV-associated nephropathy (HIVAN) causing proteinuric kidney disease; osteoporosis and fractures; non-AIDS malignancies (lung, anal, and cervical cancers are significantly more common). ART complications: tenofovir-related nephrotoxicity and reduced bone density; abacavir hypersensitivity (HLA-B*57:01 screening mandatory); dyslipidaemia, insulin resistance, and lipodystrophy with older regimens. With effective ART, life expectancy is now near-normal in people who are diagnosed promptly and adhere to treatment.

Prevention of HIV transmission — multiple effective interventions: U=U (Undetectable = Untransmittable): a person on ART with a sustained undetectable viral load (below 200 copies/mL — below 50 copies/mL in UK guidelines) cannot sexually transmit HIV; PARTNER and PARTNER2 studies (2016, 2019) — 0 transmissions from HIV-positive partners with undetectable viral load over 77,000+ condomless sex acts; U=U endorsed by BHIVA, UNAIDS, and all major HIV organisations; having an undetectable viral load is the most effective HIV prevention tool. Condoms: male (external) and female (internal) condoms — highly effective barrier against HIV and other STIs when used correctly and consistently. PrEP (Pre-Exposure Prophylaxis): TDF/FTC once daily or 2-1-1 method for MSM — 99% reduction in HIV risk; available free on NHS at sexual health clinics; recommended for HIV-negative people at substantial risk. Harm reduction for PWID: sterile needle/syringe distribution; opioid substitution therapy (methadone, buprenorphine); naloxone distribution. Voluntary medical male circumcision (VMMC): reduces HIV risk by 60% in heterosexual men — rolled out in sub-Saharan Africa. MTCT prevention: ART for all HIV-positive pregnant women throughout pregnancy; tenofovir + lamivudine or zidovudine + lamivudine for baby post-delivery; formula feeding or safe breastfeeding counselling; caesarean section if viral load above 50 copies/mL at 36 weeks — reduces mother-to-child transmission to below 1%. Regular STI testing: reduces undiagnosed STIs which increase HIV susceptibility and infectivity.

Seek emergency medical care immediately for: severe breathlessness with dry cough and fever in a person with HIV or suspected HIV — possible Pneumocystis jirovecii pneumonia (PCP) — requires urgent hospitalisation, IV co-trimoxazole, and oxygen; severe headache, neck stiffness, and photophobia with fever — cryptococcal meningitis emergency (diagnosis by LP — India ink stain, cryptococcal antigen; IV liposomal amphotericin B treatment); confusion, focal neurological deficit, or seizures with known HIV — toxoplasma encephalitis, progressive multifocal leukoencephalopathy (PML), or CMV encephalitis; any rapidly deteriorating neurological or respiratory symptoms in someone with low CD4 count. See a sexual health clinic or GP urgently for: suspected HIV exposure in the last 72 hours — attend sexual health clinic immediately for nPEP (post-exposure prophylaxis); flu-like illness 2-4 weeks after unprotected sex with a possibly HIV-positive partner — possible acute HIV seroconversion — early diagnosis allows immediate ART and prevents onward transmission. Regular testing: for anyone sexually active at higher risk — HIV testing every 3-12 months at sexual health clinic.