HIV/AIDS — Transmission, CD4 Count, ART & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Human immunodeficiency virus (HIV) is a retrovirus that attacks CD4 T-lymphocytes — key cells of the immune system — progressively impairing immune defenses. Without treatment, HIV leads to acquired immunodeficiency syndrome (AIDS), defined by a CD4 count below 200 cells/µL or the presence of AIDS-defining illnesses. Approximately 39.9 million people live with HIV globally. With modern antiretroviral therapy (ART), HIV is now a manageable chronic condition — people with HIV on effective treatment have near-normal life expectancy and cannot transmit the virus sexually. The WHO 90-90-90 targets (90% of people living with HIV knowing their status, 90% of those on ART, 90% of those virally suppressed) have been largely achieved in high-income countries but remain challenging globally. HIV-1 is responsible for the global pandemic; HIV-2, more common in West Africa, progresses more slowly but is intrinsically resistant to NNRTIs. Long-acting injectable ART regimens (cabotegravir + rilpivirine given monthly or bimonthly) have improved adherence and patient satisfaction for stable patients who cannot adhere to daily oral regimens.

HIV is transmitted via contact with infected blood, semen, vaginal secretions, rectal secretions, and breast milk. Routes of transmission include unprotected sexual intercourse (anal sex carries highest risk, followed by vaginal sex), sharing needles and drug equipment, blood transfusions with unscreened blood, needle-stick injuries, and mother-to-child transmission (during pregnancy, delivery, or breastfeeding). High-risk groups include men who have sex with men (MSM), people who inject drugs, sex workers, transgender women, and sexual partners of HIV-positive individuals. HIV is NOT transmitted by casual contact, saliva, hugging, sharing dishes, or mosquito bites. Perinatal transmission risk depends on maternal viral load at delivery — undetectable maternal viral load reduces transmission risk to below 1%. Vertical transmission routes include transplacental during pregnancy (most common), intrapartum during delivery (major route), and postnatal through breastfeeding (continuing risk throughout breastfeeding period). Pre-chewing (pre-mastication) of food for infants by an HIV-infected caregiver is a rare but documented transmission route.

Acute HIV infection (2–4 weeks after exposure) causes a flu-like 'seroconversion illness': fever, pharyngitis, rash (maculopapular rash on trunk), lymphadenopathy, myalgia, headache, and oral ulcers — often mistaken for mononucleosis. After this acute phase, a clinically asymptomatic period lasting years follows despite ongoing viral replication. As CD4 count falls below 200 cells/µL (AIDS), opportunistic infections and AIDS-defining cancers develop: Pneumocystis jirovecii pneumonia (PCP), toxoplasmosis, cryptococcal meningitis, CMV retinitis, tuberculosis, Kaposi's sarcoma, and non-Hodgkin lymphoma. Opportunistic infections by CD4 threshold: CD4 below 500 — HIV-associated nephropathy, cardiovascular disease acceleration; CD4 below 200 — Pneumocystis jirovecii pneumonia (PCP), Kaposi's sarcoma, recurrent bacterial pneumonia, cerebral toxoplasmosis; CD4 below 100 — cryptococcal meningitis, disseminated Mycobacterium avium complex (MAC); CD4 below 50 — cytomegalovirus (CMV) retinitis, progressive multifocal leukoencephalopathy (PML). AIDS-related lymphoma (non-Hodgkin's) is an AIDS-defining condition occurring at varying CD4 levels.

HIV testing uses fourth-generation combined antigen/antibody tests — detecting both HIV antibodies and p24 antigen — with a window period of 45 days for virtually all infections. A reactive test is confirmed by a supplemental antibody differentiation assay distinguishing HIV-1 from HIV-2. HIV RNA PCR (viral load) quantifies viral replication and monitors treatment response. CD4 lymphocyte count assesses immune status and guides prophylaxis decisions. Genotypic resistance testing guides ART selection. Routine baseline investigations include STI screening, hepatitis B/C serology, TB screen, CBC, renal and liver function, and lipids. WHO recommends universal HIV testing for all adults in high-prevalence settings. Post-exposure prophylaxis (PEP) effectiveness monitoring: HIV RNA at baseline, 4 weeks, and 12 weeks post-exposure (HIV antibody testing at 45 days if 4th-generation test used); creatinine, hepatitis B surface antigen before starting tenofovir-containing PEP. HIV drug resistance testing using genotypic resistance assays identifies mutations conferring resistance to specific antiretroviral drug classes — essential before ART initiation if transmitted drug resistance is suspected (transmitted resistance prevalence is 10–15% in some settings).

All HIV-positive individuals should start ART regardless of CD4 count — ideally on the day of diagnosis ('rapid ART start'). Modern first-line ART regimens use 2 or 3 drugs to suppress viral replication to undetectable levels (below 50 copies/mL). Preferred first-line regimens include dolutegravir-based combinations (dolutegravir/lamivudine; bictegravir/tenofovir alafenamide/emtricitabine) — once-daily single-tablet regimens with excellent tolerability and high genetic barrier to resistance. Undetectable = Untransmittable (U=U): people with undetectable viral load on stable ART cannot sexually transmit HIV. PrEP (pre-exposure prophylaxis) with oral tenofovir/emtricitabine or injectable cabotegravir reduces HIV acquisition risk by over 99% in high-risk individuals. Bictegravir/tenofovir alafenamide/emtricitabine (BIC/TAF/FTC — Biktarvy) is currently the most commonly used single-tablet regimen globally — high genetic barrier to resistance, minimal drug interactions, excellent renal and bone safety profile of TAF compared to tenofovir disoproxil fumarate. Long-acting cabotegravir + rilpivirine (Cabenuva) injections given every 4 or 8 weeks have non-inferior virological outcomes to daily oral therapy and provide significant patient satisfaction improvements. CD4 count recovery with suppressive ART: expect 100–150 cells/µL increase per year in the first 2 years — patients with CD4 below 200 at ART initiation require Pneumocystis prophylaxis (co-trimoxazole) until CD4 exceeds 200 for 3 months.

Without ART, AIDS-defining opportunistic infections are the primary cause of mortality. Even with ART, HIV-positive people have increased risk of non-AIDS conditions: cardiovascular disease (2-fold higher), renal impairment, liver disease, osteoporosis, and non-AIDS cancers (anal, lung, cervical) from immune dysregulation and coinfections. Immune reconstitution inflammatory syndrome (IRIS) occurs as CD4 counts recover rapidly after starting ART, triggering paradoxical worsening of previously subclinical opportunistic infections. Long-term ART may cause metabolic side effects including dyslipidemia, insulin resistance, and rare renal or bone toxicity depending on the agent used.

Consistent correct condom use significantly reduces sexual transmission. PrEP (oral daily or injectable every 2 months cabotegravir) for HIV-negative individuals at high risk eliminates acquisition risk when used consistently. Post-exposure prophylaxis (PEP) — a 28-day ART course — prevents infection if started within 72 hours of high-risk exposure. Harm reduction for people who inject drugs: clean needle programs, opioid substitution therapy, and PrEP. Mother-to-child transmission is prevented by maternal ART throughout pregnancy, intrapartum prophylaxis, and infant ART for 4–6 weeks after birth — reducing transmission to below 1%. Partner testing and immediate treatment of all HIV-positive individuals (TasP — treatment as prevention) are the pillars of ending the global epidemic.

Seek urgent medical attention for: potential HIV exposure in the last 72 hours — start post-exposure prophylaxis (PEP) within 72 hours (earlier is better; ineffective after 72 hours); fever, rash, sore throat, and lymphadenopathy 2-4 weeks after potential exposure (possible acute HIV seroconversion — test immediately); or any opportunistic infection symptom in a known HIV-positive patient (Pneumocystis pneumonia, CMV retinitis, cryptococcal meningitis). Get tested for HIV if: you have had unprotected sex with a new partner; you share injecting equipment; or you are pregnant. HIV testing is the entry point to life-saving treatment. Discuss PrEP with a sexual health clinic or GP if you are in a high-risk group — PrEP is highly effective and available on the NHS in England.