Around 83,000 people in the UK are living with HIV. According to the Health Protection Agency (now Public Health England), around a quarter (27%) don't know they have the virus.
Dr Valerie Deplech, an HIV expert at the Health Protection Agency, says: "We are seeing an ever-increasing pool of people living with HIV and AIDS in the UK."
HIV attacks the immune system, the body's defence against infection and disease. This means someone with HIV has a higher risk of getting a serious infection or disease, such as cancer.
Take the sexual health self-assessment test to see if your sex life is putting you at risk of contracting HIV.
How do people get HIV?
HIV is spread through bodily fluids, such as semen or blood. It's most commonly passed on during unprotected sex, including oral and anal sex. It can also be passed on through sharing sex toys.
Who gets HIV?
Anyone can get HIV if they have unprotected sex, but gay men are one of the highest risk groups. Women who have only ever had sex with women are at low risk.
Can I get HIV from kissing someone with it?
You can't catch HIV by kissing someone. Nor can you catch it if someone with HIV sneezes on you, from sharing a bath, towels or cutlery with someone who has HIV, or by sitting on a toilet seat someone with HIV has used.
How can I avoid getting HIV?
Using a condom during sex is the best way to avoid getting HIV, as well as other sexually transmitted infections (STIs). Don't use an oil-based lubricant as it can damage the condom, making it more likely to split. Use a water-based lubricant, such as KY Jelly, instead.
If I get HIV, can't I just take a few pills to make me better?
Gary Williams, from Birmingham's Healthy Gay Life Project, says: "The reality of HIV infection is that you need blood tests every six months (sometimes more often) and you could be taking up to 12 pills a day. People are living a long time, but their quality of life is compromised."
How can I get tested for HIV?
A simple blood test can determine whether you have HIV. It can take up to three months after infection to detect the virus, so you may need to have another test to be sure. There are various places you can get tested, including your GP surgery or a genitourinary medicine (GUM) clinic.
When should I get a test?
If you're a gay man and you've had unprotected sex, it's important that you have a test. Public Health England recommends annual HIV testing for gay men who change sexual partners.
What will happen if the test result is positive?
If your test is positive, you'll be referred to an HIV clinic. HIV clinics employ professionals who specialise in helping people living with HIV.
For more information, see the Health A-Z topic about Treatment for HIV.
While there's no cure for HIV, there are medications that can slow its progression and prolong life.
Read the answers to more frequently asked questions about HIV and AIDs.
Now, read an article on sexual health for gay and bisexual men.