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HIV & AIDS glossary

word cloud of HIV related terms


Adherence means taking HIV treatment exactly as you are told to (like time of day, frequency, with or without food, and so on). Poor adherence can lead to drug resistance which means the treatment will stop working. It’s particularly important to make sure you don’t run out of drugs, as any extended breaks in treatment will be more damaging than taking treatment a bit late one day.


AIDS stands for Acquired Immune Deficiency Syndrome and is a set of symptoms and illnesses that occur at the very final stage of HIV infection. It is diagnosed when a person’s immune system is almost entirely destroyed, and too weak to fight off infections.

Antiretroviral drugs (ARVs)

These are drugs used to treat HIV and prevent it from copying itself and spreading throughout the body. They keep the virus at low levels, improve the immune system, and reduce the likelihood of passing HIV on to someone else.

Antiretroviral treatment (ART)

This is the treatment for HIV – made up of antiretroviral drugs. ART uses a combination of three or more antiretroviral drugs (ARVs) to stop HIV from spreading throughout the body.

CD4 count

CD4 count is a measure of the number of CD4 cells (or T-helper cells) in someone’s blood. A simple blood test can count the number of cells. CD4 cells are a type of immune system cell in the body that HIV attacks and kills over time.


This is when someone has more than one serious infection at the same time. For example, when a person with HIV also has tuberculosis (TB), they are said to have an HIV/TB co-infection. This can make treatment for both infections more difficult, but also more important.


This describes someone who has two or more diseases or health conditions at a time. For example, a person with HIV may also have high blood pressure.

Drug resistance

If someone with HIV doesn’t take their treatment properly, the drugs may become unable to control the virus which can cause the treatment to stop working. It is also possible that a person who has developed a strain of HIV that is resistant to one or more drugs can transmit this drug-resistant strain to another person.

False negative result

When a person has HIV but an HIV test indicates they don’t have it, it's called a false negative result. This usually happens during the ‘window period’ immediately after initial infection when the body’s reaction to the virus is still undetectable from a blood test.

False positive result

When a person does not have HIV but an HIV test indicates they do, it's known as a false positive result. In this case another test would be carried out to confirm the result.

First-line treatment

The initial treatment recommended for HIV is made up of three or more antiretroviral drugs from two different drug classes. This is known as first-line treatment.


HIV stands for Human Immunodeficiency Virus. It attacks a person’s immune system cells, and without treatment will completely destroy their immune system and their ability to fight off infections.

Post-exposure Prophylaxis (PEP)

PEP is short-term treatment that must be taken within 72 hours of possible exposure to HIV, for example after unprotected sex. It stops HIV spreading throughout the body and causing an infection.

Pre-exposure Prophylaxis (PrEP)

PrEP is a daily course of antiretroviral drugs that can prevent HIV infection. It is aimed at HIV-negative people who may have an HIV-positive partner, be unable to negotiate condom use, or be having repeated sex without a condom. When PrEP is adhered to exactly as prescribed, it reduces the chances of HIV infection to near-zero. But if pills are missed then the risk of infection will increase substantially. Read more about PrEP.

Opportunistic infection

This is a type of infection that occurs in people with a weakened immune system (for example people living with HIV).

Second-line treatment

A course of antiretroviral drugs that is taken if first-line treatment has stopped working is called second-line treatment.

Serodiscordant couple

A serodiscordant couple is when one person has HIV and the other does not. Also known as a discordant couple, a serodifferent couple, or a mixed-status couple.

Sexually transmitted infection (STI)

STIs are infections that are passed on during sexual contact. Examples include chlamydia, gonorrhoea and trichomoniasis.

T-helper cells

See CD4 count above.

Third-line treatment

A course of antiretroviral drugs that is taken if second-line treatment has stopped working is called third-line treatment.

Undetectable / virally suppressed

A person living with HIV is considered to have an ‘undetectable’ viral load – or to be virally suppressed – when antiretroviral treatment has brought the level of virus in their body to such low levels that blood tests cannot detect it. As long as treatment is adhered to and viral load remains undetectable (as monitored by a health professional), they cannot transmit HIV to others and their health is not affected by HIV.

Viral load

Viral load is the amount of virus in the blood. It is measured by a simple blood test. It indicates how well a person’s antiretroviral treatment is working.

Window period

The time between HIV infection and when the body produces enough HIV antibodies to be detected by an HIV test is called the window period. This is between 2 and 12 weeks depending on the type of test.

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Last full review: 
14 February 2017
Next full review: 
14 February 2020

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Last updated:
05 June 2017
Last full review:
14 February 2017
Next full review:
14 February 2020