What is the difference between HIV and AIDS?

What is the distinction between HIV and AIDS, and what might be behind the recent reduction in new infections? Chris Smith was joined by Laura Waters from Mortimer Market Centre, a sexual health clinic in London.

Laura - HIV is a virus. It’s an infectious particle. It stands for Human Immunodeficiency Virus and it’s an infection that’s spread primarily through sex and it enters the body and it targets a type of white blood cell. White blood cells are cells in the body that are responsible for fighting infection. It enters a particular type of white blood cell called a CD4 cell and the best way to describe these cells really is that they’re like the conductors of an orchestra. If you whole immune system, which is lots of types of cells and proteins and chemicals is an orchestra, the CD4 cell’s a conductor.

Now HIV enters these cells and it uses the cells to replicate itself but destroys them in that process and, over time, it greatly damages the immune system leaving somebody susceptible to serious infections. Symptoms like diarrhoea, weight loss and particular types of cancers, and it’s that constellation of conditions that is AIDS (Acquired Immune Deficiency Syndrome). Many people with HIV never develop AIDS because we diagnose it, and treat it before the immune system can be damaged enough to allow AIDS conditions to take hold.

Chris - How long generally elapses between a person acquiring the infection and then developing those symptoms of AIDS assuming that they don’t get diagnosed and treated?

Laura - How long it takes someone to develop AIDS will vary, and it depends mainly on that individual's immune system which is governed mainly by their own genetics. So it can be anything from two or three years through to ten, fifteen, or even years. There’s a small proportion of people who actually keep the virus under control and remain quite healthy for decades but, on average, it will typically be between five and ten years after getting the infection that people start to get sick.

Chris - If HIV is an infection of the blood stream and it’s harboured by immune cells in the blood stream, how does it come to be transmitted through sexual activity?

Laura - The virus itself, although it replicates inside immune cells, it basically travels around every body fluid. It gets into every single part of the body. You can find it spinal fluid, you find it in blood, you find it in the gut, and you find it in sexual fluids as well. So you find it in semen, you find it in viginal fluids, and you find it in rectal fluids as well. So, although it’s replicating in the immune cells, it’s floating around the body everywhere.

Chris - When a person becomes infected, how would they know?

Laura - When people first get infected, it’s a viral illness like any other viral illness so many people develop non-specific viral symptoms: fevers, rash, high temperatures, enlarged lymph glands. But this may be dismissed as just a viral illness which, in many ways, is correct, it’s just that no-one’s thought to test for HIV. At least half of people will have something that, when they look back, was a significant more severe than usual viral flu-like illness. Then, typically, there’ll be no symptoms at all until the manifestations of a damaged immune system start to become apparent.

Chris - If a person does suspect they might have contracted it and they come to a clinic like yours, how do you diagnose it?

Laura - It depends on timing. Most clinics now use point of care tests - that’s a finger prick or saliva test where you get an immediate result. But most of those tests use slightly older technology so it can take up to 12 weeks for a test to show up as positive. So if someone was infected today, with some of those point of care tests, it could be three months later before that shows up on those tests.

If somebody has suspected early HIV, so they have symptoms consistent with early HIV, they’ve had a risk exposure to HIV, then we do a standard blood test where you take blood from a vein in the arm. That’s sent to the lab where we do more detailed tests and more sensitive tests and those will show up positive for most people within four weeks.

Chris - Your clinic is one of the centres that seen a very dramatic reduction in the numbers of cases being diagnosed. Put some numbers on it for us and also tell us why you think that is?

Laura - Our clinic, the Mortimer Market Centre, has collected data along with three other big central London clinics, and that’s 56 Dean Street, Homerton, and Barts Health and we all saw a 40 per cent reduction in new HIV cases in 2016 compared to 2015. Why we think that is is a number of reasons. Now the reason that’s being most discussed is the advent of Pre-exposure Prophylaxis or PreP, so taking HIV drugs before an exposure to reduce the risk of getting HIV and it’s thought that that’s led to this sudden, dramatic downturn in new diagnoses.

Other important factors are the fact that we have fewer and fewer undiagnosed people. We know in gay men who are the biggest risk group for new HIV in the UK, most infections come from people who don’t know they have the virus, so these are undiagnosed people who are responsible for transmitting most of the new virus onwards. And, actually, the undiagnosed proportion has come down so now only 13 percent of people with HIV in the UK are estimated to not know their status. Now that’s still too high but it’s the lowest it's been in some time. So by testing and knowing your status you are less likely to pass the virus on to somebody else.

The other important factor is treatment. People with HIV who are on treatment have a zero, or close to zero chance of passing the virus on to sexual partners. About 94 per cent of people with HIV are on treatment and undetectable. So it’s a combination of PrEP, better diagnosis, and the fact that people with HIV are on treatment that keeps the virus suppressed and means the risk of passing it on is very, very, very, low...