The infection
HIV is a retrovirus that progressively destroys CD4 lymphocytes, the coordinating cells of the immune system. Untreated, that damage leads after several years to AIDS, the stage defined by opportunistic infections and certain cancers. With antiretroviral treatment that course is no longer inevitable: someone diagnosed early and treated has a life expectancy comparable to the general population.
Key facts
| Organism | Retrovirus, mainly HIV-1 |
|---|---|
| Seroconversion illness | Flu-like illness two to four weeks after exposure, in about half of cases |
| Reliable testing from | Six weeks with a laboratory combined test, three months with a rapid test |
| Curable | No, but fully controlled on treatment |
| Undetectable viral load | The virus is not transmitted sexually |
| Prevention | Condoms, PrEP, post-exposure treatment |
| Emergency treatment | Ideally within four hours, at the latest 48 to 72 |
How it is transmitted
The virus passes through blood, semen, vaginal and rectal fluids, and breast milk. Unprotected anal sex carries the highest risk, followed by vaginal sex; oral sex carries a low but not zero risk. Sharing injecting equipment is high risk. Mother-to-child transmission, once common, is now almost entirely preventable where the mother is tested and treated. HIV is not transmitted by saliva, tears or ordinary contact.
Symptoms
Two to four weeks after infection, about half of people have a seroconversion illness: fever, fatigue, swollen glands, sore throat and rash, a picture resembling flu or glandular fever that very often passes unremarked. A symptom-free phase then follows, potentially for years, during which the virus multiplies and remains transmissible. Symptoms return only at an advanced stage, when immunity is already badly damaged.
Testing
The reference test is a laboratory combined assay detecting both antibodies and p24 antigen; it is reliable six weeks after exposure. Rapid tests and self-tests, which detect antibodies only, are reliable at three months. PCR can detect the virus earlier, typically from ten to fifteen days, but is reserved for particular situations. Testing is free and anonymous at dedicated services, and self-tests are sold in pharmacies.
Treatment
Antiretroviral treatment combines several molecules, usually in a single daily tablet; long-acting injectable forms given every two months also exist. It makes the viral load undetectable within weeks to months. It must be taken without interruption: stopping allows the viral load to rebound and the virus becomes transmissible again. Follow-up involves regular viral load and CD4 monitoring.
If left untreated
Without treatment, falling CD4 counts expose people to opportunistic infections — pneumocystis pneumonia, cerebral toxoplasmosis, tuberculosis — and to certain cancers, defining AIDS. With early, sustained treatment these do not occur. The focus then shifts to ageing, cardiovascular risk and drug interactions, which form part of long-term care.
Prevention
- Condoms remain effective and protect against other sexually transmitted infections at the same time.
- PrEP, preventive treatment taken by an HIV-negative person, is highly effective, either daily or on demand.
- Post-exposure treatment should start as soon as possible, ideally within four hours and at the latest 48 to 72 hours, from emergency services.
- A treated person with an undetectable viral load does not transmit the virus sexually: this is an established scientific finding.
What has changed recently
Very long-acting injectable prevention has been evaluated and authorised: a six-monthly injection showed close to complete efficacy in trials published in 2024, opening the way to prevention that no longer depends on a daily tablet.
After a diagnosis
- Start treatment promptly: there is no longer any reason to wait for CD4 counts to fall.
- Notify partners so they can test, with help from the service if the conversation is difficult.
- Accept support: community organisations and specialist clinics matter well beyond the medical side.
- Tell any prescriber about your treatment: drug interactions are numerous.
Worth remembering
Emergency treatment after an exposure only works in the first hours. Do not leave it until tomorrow: beyond 48 to 72 hours it is no longer offered.
Also in this section
HIV in children
A child is not a small adult: they are infected differently, their viral load is higher, and their treatment depends on someone else.
Seventy-eight children, 1993-1998
A cohort followed for six years at a Paris hospital, at the exact moment paediatric HIV turned.
Mother-to-child transmission
What happens during delivery, the mode of delivery, newborn prophylaxis and infant feeding.
A little history
On 5 June 1981 the weekly bulletin of the CDC in Atlanta reported five cases of a rare pneumonia in young gay men in Los Angeles: the first official signal of the epidemic. The virus was isolated in 1983 at the Institut Pasteur by Françoise Barré-Sinoussi and Luc Montagnier (Nobel Prize 2008), then by Robert Gallo's team in 1984; it received its definitive name, HIV, in 1986. We now know that HIV-1 comes from a chimpanzee virus of south-eastern Cameroon that crossed into humans in the early twentieth century; the oldest positive human sample dates from 1959, in Kinshasa, where the epidemic smouldered for decades before being noticed.
The early years were those of near-certain death and of stigma. AZT, the first treatment, arrived in 1987 with limited effect; the turning point was 1996, when the combination therapies presented at the Vancouver conference turned a fatal disease into a chronic one. Then came one-pill-a-day treatments, pre-exposure prophylaxis (PrEP, approved in the United States in 2012), the message "undetectable = untransmittable" validated by the studies of the 2010s, and in 2025 the first twice-yearly preventive injections.
The toll remains immense: more than 44 million deaths since the start of the epidemic according to UNAIDS, and around 41 million people living with the virus today, nearly three quarters of them on treatment. No vaccine has yet succeeded; a handful of cures after bone-marrow transplants (the "Berlin patient", 2008) show the idea is not absurd, but they remain exceptional.
Country by country
The medicine is the same everywhere, but access, prevention programmes, what is free of charge and which services are responsible differ completely. Each country below has its own page.
Select a country to open its detailed page.