STI Guide

HIV

Human Immunodeficiency Virus. A serious but highly treatable infection. Early diagnosis, PEP after exposure, and modern antiretroviral therapy have transformed outcomes.

Human Immunodeficiency Virus

HIV is a virus that attacks CD4 cells — a type of white blood cell essential to the immune system. Without treatment, HIV can progress to AIDS (Acquired Immunodeficiency Syndrome). With modern antiretroviral therapy (ART), people with HIV can expect a near-normal life expectancy and those who are undetectable cannot transmit the virus sexually.

Testing window (4th gen)45 days
Confirmatory window90 days
PEP windowWithin 72 hours
CurableNo — but fully treatable
Undetectable = UntransmittableU=U confirmed

Key facts about HIV

Modern ART allows people with HIV to live long, healthy lives.

PEP (Post-Exposure Prophylaxis) can prevent infection if started within 72 hours of exposure.

PrEP (Pre-Exposure Prophylaxis) is highly effective at preventing HIV in high-risk individuals.

Someone with an undetectable viral load cannot sexually transmit HIV (U=U).

HIV is transmitted through blood, sexual fluids, and breast milk — not through casual contact.

Most fourth-generation HIV tests are conclusive at 45 days; a negative result at 90 days is definitive.

How is HIV transmitted?

HIV is transmitted through specific bodily fluids: blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk. The most common routes of transmission are unprotected anal or vaginal sex, sharing needles or syringes, and from a parent to a child during pregnancy, birth, or breastfeeding. HIV cannot be transmitted through saliva, tears, sweat, toilet seats, or casual contact.

What are the symptoms of HIV?

In the first 2–4 weeks after infection, around 80% of people experience an acute illness called seroconversion, which can resemble a severe flu: fever, swollen glands, sore throat, rash, muscle aches, and fatigue. These symptoms typically resolve within a few weeks. After this, HIV often causes no symptoms for many years, which is why testing is so important following any risk exposure.

HIV testing: when and what kind?

Fourth-generation (antigen/antibody combination) tests are the standard and can detect HIV around 18–45 days after exposure, with the vast majority of infections detectable by 45 days. A negative result at 45 days is highly reassuring; a definitive negative result at 90 days rules out infection for almost all scenarios. Rapid point-of-care tests exist but have longer window periods — confirm with a lab test.

What is PEP?

Post-Exposure Prophylaxis (PEP) is a 28-day course of antiretroviral medication taken after a potential HIV exposure. It works by preventing the virus from establishing a permanent infection. PEP must be started within 72 hours of the exposure — the sooner the better. It is available from A&E departments, sexual health clinics, and some GUM clinics. PEP is not a substitute for regular prevention strategies.

What is PrEP?

Pre-Exposure Prophylaxis (PrEP) is a medication taken by HIV-negative people before potential HIV exposure to prevent infection. When taken correctly, PrEP is more than 99% effective at preventing HIV from sex. In the UK, PrEP is available on the NHS for people assessed as being at high risk of HIV. It does not protect against other STIs.

HIV treatment

Antiretroviral therapy (ART) suppresses HIV to undetectable levels in the blood. People on effective ART cannot sexually transmit HIV to partners (Undetectable = Untransmittable, or U=U). Treatment today typically involves one tablet per day and has minimal side effects for most people. Starting treatment early is strongly recommended.

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