HIV and AIDS: what they are, symptoms, how HIV spreads, testing and treatment

Terrence Higgins Trust explains that HIV stands for human immunodeficiency virus, where "immunodeficiency" refers to the weakening of the immune system by the virus. AIDS stands for acquired immune deficiency syndrome and is a collection of illnesses caused by the virus. You cannot be diagnosed with AIDS unless you are already HIV positive.

In the 1980s and early 1990s most people with HIV were eventually diagnosed with AIDS. Now, thanks to modern antiretroviral treatment, very few people in the UK develop serious HIV-related illnesses. Terrence Higgins Trust says the term AIDS is not used much by UK doctors, who talk about late-stage or advanced HIV instead.

The NHS says the symptoms of HIV are different for everyone. Some people experience a short flu-like illness around 2 to 6 weeks after infection. Terrence Higgins Trust calls this a seroconversion illness: it lasts one or two weeks, happens to most but not all people, and can be severe enough to put someone in hospital or so mild it is mistaken for flu, although a blocked or runny nose is not usually a symptom.

After that you may have no other symptoms for years, which means many people with HIV do not know they have it. If HIV is not treated it damages your immune system and may eventually cause more serious illnesses, such as tuberculosis, pneumonia or cancer. Terrence Higgins Trust lists later signs as weight loss, night sweats, thrush in the mouth, more frequent herpes or cold sores, swollen glands in the groin, neck or armpit, long-lasting diarrhoea and tiredness, noting that people without HIV can also get any of these, so testing is the only way to know.

• Early (2 to 6 weeks): sore throat, high temperature or fever, swollen glands, muscle aches and tiredness, and a skin rash.

• Years of no symptoms in many people.

• Later, if untreated: weight loss, night sweats, mouth thrush, more herpes outbreaks, swollen glands, long-lasting diarrhoea, tiredness.

• Advanced HIV (AIDS): serious infections such as tuberculosis and pneumonia, and some cancers.

The NHS says HIV is most often spread by having vaginal, anal or oral sex with someone who has HIV, while not using a condom, because infected body fluids get into the bloodstream. These fluids include blood, semen, vaginal fluids and mucus from inside the anus. It can also be spread by sharing needles, syringes or other injecting equipment, or sharing sex toys, with someone who has a detectable viral load, and to a baby during pregnancy or birth if the mother has a detectable viral load.

The NHS is clear that you cannot get HIV from kissing, hugging or shaking hands, or from sharing toilet seats, food, drinks or normal everyday household items like cups and cutlery. Terrence Higgins Trust adds that HIV is not passed on by spitting, sneezing or coughing, and cannot survive for very long outside the body. It says someone with a detectable viral load can pass on HIV through blood, semen, vaginal fluid, anal mucus and breast milk.

The NHS says that if you are having effective treatment and have an undetectable viral load, you cannot pass HIV on to someone else. Terrence Higgins Trust says studies have shown this, and that it can take up to six months from starting treatment to become undetectable. Since 1985 donated blood in the UK has been tested for HIV, making the risk from a transfusion very low.

HIV is caused by the virus itself. The NHS says you may be at higher risk if you have a current or previous partner with HIV, are from a country with high HIV rates, are a man who has sex with men without a condom, are a woman who has sex with men who have sex with men without a condom, are a trans woman, have had many sexual partners, engage in high-risk activities such as chemsex, or have other sexually transmitted infections, inject recreational drugs, are a sex worker, have been raped, or have received a blood transfusion or been exposed to infected blood or tissue in a country without effective HIV screening.

The NHS says there is a possible but very low risk if a healthcare professional accidentally pricks themselves with an infected needle at work.

The NHS says HIV tests use saliva from your mouth or blood from your finger. A clinic usually sends the sample to a laboratory with a result within a few days, while a home testing kit is often available within a few minutes. You can get a test from a GP or sexual health clinic, clinics run by charities such as Terrence Higgins Trust, some family planning clinics, antenatal clinics, local drug services, pharmacies that provide home kits, or private clinics where you pay. The NHS says make sure a home kit is clearly marked for self-testing, has a CE mark and an intact seal.

Terrence Higgins Trust explains the window period: national testing guidelines set a 90-day window for self-tests, while blood tests at clinics or sent to a lab have a testing window of 45 days. Within the window you might have HIV but not enough antibodies for a test to detect it. If you test at a sexual health clinic, testing centre or GP the test is free; a private clinic charges.

The NHS says a negative result means no signs of infection, and you may be advised to retest a few weeks later. A positive result means you could have HIV and needs a confirming blood test at a clinic; if that is positive you are referred to an HIV clinic. Pregnant women are offered an HIV blood test as part of routine antenatal screening.

The NHS says condoms are the most effective protection against HIV and other STIs, and to use water-based lubricants as oil-based ones can make condoms break. PrEP (pre-exposure prophylaxis) is available free on the NHS from sexual health clinics for people at higher risk. It usually comes as tablets taken every day or on demand, though some people may need an injection every two months instead.

PEP (post-exposure prophylaxis) is medicine to take if you think you have been exposed to HIV in the last 72 hours. It is available from sexual health clinics and A&E, and may stop you getting infected. If you think you were exposed more than 72 hours ago, see a GP or sexual health clinic for a test. Do not share needles, syringes, spoons or swabs.

The NHS says there is currently no cure for HIV, but there are treatments to reduce the amount of HIV in your blood. You are seen at a specialist HIV clinic. HIV is treated with antiretrovirals, tablets you take every day, to bring the amount of virus down to an undetectable viral load. If you take daily medicines it usually takes around 6 months for the virus to become undetectable.

Terrence Higgins Trust says treatment guidelines recommend that everyone with HIV starts treatment right away. Once on effective treatment with an undetectable viral load you cannot pass on HIV and your health is protected. It says side effects are not inevitable and if they occur are generally mild and easy to treat, that some HIV drugs interact with over-the-counter medicines, recreational drugs and herbal supplements, and that taking treatment properly matters because poor adherence can lead to drug resistance.

The NHS says most people with HIV who have the correct treatment do not go on to develop AIDS and can live a long and healthy life. You will be offered counselling, and need to tell your partner and any recent sexual partners who may have been exposed.

The NHS says HIV can be passed to a baby during pregnancy or birth if the mother has a detectable viral load, and pregnant women are offered an HIV test as part of antenatal screening. Terrence Higgins Trust says being on HIV treatment with an undetectable viral load lowers the chance of the baby being born with HIV to just 0.1%, and that following medical advice closely protects the baby from transmission during pregnancy, birth and breastfeeding.

The NHS says go to a sexual health clinic if you think you have been exposed to HIV in the last 72 hours; staff can offer emergency HIV medicine (PEP). You can also get it from your nearest A&E. For a flu-like illness after a possible exposure, tell whoever tests you so the right type of test is used.

HIV testing, PrEP, PEP, treatment and care are available free through NHS sexual health clinics and HIV clinics, and testing is free at a GP or sexual health clinic. Private clinics charge for testing. Charities such as Terrence Higgins Trust and the National AIDS Trust provide information and support.