Human immunodeficiency virus (HIV)

If you may have been exposed to HIV within the past 72 hours, seek urgent medical care now and ask about post-exposure prophylaxis (PEP). PEP should be started as soon as possible—ideally within 24 hours and no later than 72 hours—without waiting for routine test results when a clinician considers the exposure significant. If you are very unwell, have severe breathing difficulty, confusion, a seizure, fainting or a new neurological symptom, seek emergency care.

What are HIV and AIDS?

Human immunodeficiency virus (HIV) attacks immune cells, especially CD4 T cells. Without effective treatment, progressive immune damage can allow serious infections and some cancers to occur. Acquired immunodeficiency syndrome (AIDS) is the most advanced stage of HIV infection, defined by particular illnesses or severe immune suppression; it is not a separate virus. Many people diagnosed early and taking effective antiretroviral therapy (ART) never develop AIDS and can live long, healthy lives.

There is currently no widely available cure, but ART can suppress HIV to an undetectable level on standard blood tests. Treatment protects health and, when an undetectable viral load is maintained, prevents sexual transmission—known as Undetectable = Untransmittable, or U=U.

How HIV is and is not transmitted

HIV can be transmitted when blood, semen, pre-seminal fluid, rectal fluid, vaginal fluid or breast milk containing the virus reaches a mucous membrane, damaged tissue or the bloodstream. The most common routes are anal or vaginal sex without an effective prevention method and sharing needles, syringes or other injection equipment. Transmission can also occur during pregnancy, birth or breastfeeding, though treatment and coordinated perinatal care greatly reduce this risk.

HIV is not spread by hugging, shaking hands, sharing toilets, dishes or food, insect bites, sweat, tears, ordinary kissing or saliva. It does not reproduce outside the human body. Using accurate language matters: anyone can acquire HIV, and infection is not evidence of a person's identity, character or behaviour.

Symptoms and stages

Some people develop fever, sore throat, rash, swollen glands, fatigue or muscle aches two to four weeks after infection; others have no noticeable illness. These symptoms resemble many common infections and cannot diagnose HIV. A long period with few or no symptoms may follow while untreated HIV continues to affect the immune system. Advanced disease can cause weight loss, persistent fever or diarrhoea, recurrent infections, tuberculosis, oral or oesophageal thrush, neurological illness or certain cancers. Symptoms alone cannot establish or exclude HIV.

Testing and diagnosis

An HIV test is the only way to know your status. Laboratory antigen/antibody tests, rapid or self antibody tests and nucleic-acid tests have different window periods. A test taken too soon can be negative even after infection, and PrEP or PEP can affect detection. A clinician or testing service can advise which test to use and when to repeat it. A reactive rapid or self-test needs confirmatory testing; laboratories usually perform supplemental testing after a reactive laboratory screen.

After diagnosis, initial assessment typically includes viral load, CD4 count, resistance testing, kidney and liver tests, hepatitis and other infection screening, pregnancy assessment where relevant, vaccination review and a discussion of medicines, mental health, substance use and practical barriers to care. This assessment guides treatment but should not create an unnecessary delay in starting ART.

Antiretroviral treatment

ART is recommended for everyone with HIV and should begin immediately or as soon as possible after diagnosis. It uses a combination of medicines to stop viral replication. The precise regimen is individualized according to resistance results, other conditions, pregnancy, drug interactions, side effects, access and preference. Viral load shows whether treatment is suppressing HIV; CD4 count helps assess immune function and the need for prevention or treatment of opportunistic infections.

ART is lifelong. Skipping doses or losing access can allow the viral load to rebound and drug resistance to develop. Do not stop or change treatment on your own. Tell the care team about cost, stigma, housing, mental-health concerns, side effects or difficulty remembering doses: these are reasons to add support, not to withhold treatment. If the viral load is not suppressed, clinicians check adherence, interactions, absorption and resistance and adjust care when needed.

Preventing HIV

People without HIV who may have ongoing exposure can discuss pre-exposure prophylaxis (PrEP), available as tablets or injections in some settings. PrEP greatly reduces the chance of acquiring HIV when used as prescribed but does not prevent other sexually transmitted infections or pregnancy. Condoms, sterile injection equipment, never sharing needles, regular testing and diagnosis and treatment of other sexually transmitted infections remain useful choices. PEP is an emergency 28-day course after a potential exposure, not a substitute for ongoing prevention.

For a person living with HIV, taking ART and maintaining an undetectable viral load prevents sexual transmission. Partners may still choose condoms or PrEP for additional reasons, including prevention of other infections or pregnancy. Discuss disclosure and partner services in a safe, confidential and non-coercive setting.

Pregnancy and infant feeding

HIV care before conception, during pregnancy and after birth should involve experienced maternity, HIV and infant teams. Effective ART and viral suppression greatly lower perinatal transmission. Infant-feeding advice must follow current national guidance and the family's circumstances. Properly prepared formula or pasteurized donor milk eliminates transmission through breastfeeding. With sustained viral suppression, breastfeeding transmission risk is less than 1% but not zero under current US guidance, so shared decision-making, frequent follow-up and infant testing are essential. Where safe replacement feeding is not feasible, local or WHO guidance may differ; obtain specialist advice early rather than stopping feeding abruptly.

Advanced HIV and outlook

People with advanced immune suppression may need prompt evaluation for opportunistic infections and preventive medicines based on the CD4 count, exposure history and local epidemiology. Fever, worsening cough, breathlessness, severe headache, confusion, weakness, persistent vomiting or inability to take ART warrants urgent assessment. Starting or restarting ART around some serious infections requires specialist timing, so self-treatment is unsafe.

Modern HIV care is effective. Regular viral-load monitoring, continuous access to ART, vaccination, screening and management of cardiovascular, kidney, liver, bone and mental health support wellbeing over time. Prognosis depends on individual circumstances rather than a fixed survival clock. Respectful, confidential care and community support help people stay engaged and healthy.