Definition of key terms

Consolidated ARV guidelines, June 2013


HIV refers to human immunodeficiency virus. There are two types of HIV: HIV-1 and HIV-2.

HIV-1 is responsible for the vast majority of HIV infections globally. Within these guidelines, HIV refers to both HIV-1 and HIV-2 unless otherwise specified.

Age groups and populations

The following definitions for adults, adolescents, children and infants are used to ensure consistency within these consolidated guidelines, as well as with other WHO guidelines. It is recognized that other agencies may use different definitions.

An adult is a person older than 19 years of age unless national law defines a person as being an adult at an earlier age.

An adolescent is a person aged 10 to 19 years inclusive.

A child is a person 19 years or younger unless national law defines a person to be an adult at an earlier age. However, in these guidelines when a person falls into the 10 to 19 age category they are referred to as an adolescent (see adolescent definition).

An infant is a child younger than one year of age.

These guidelines define key populations to include both vulnerable and most-at-risk populations. They are important to the dynamics of HIV transmission in a given setting and are essential partners in an effective response to the epidemic. People living with HIV are considered a key population in all epidemic contexts.

These guidelines define most-at-risk populations as men who have sex with men, transgender people, people who inject drugs and sex workers. Most-at-risk populations are disproportionately affected by HIV in most, if not all, epidemic contexts.

Vulnerable populations are groups of people who are particularly vulnerable to HIV infection in certain situations or contexts, such as adolescents (particularly adolescent girls), orphans, street children, people in closed settings (such as prisons or detention centres), people with disabilities and migrant and mobile workers. Each country should define the specific populations that are particularly vulnerable and key to their epidemic and response based on the epidemiological and social context.

Serodiscordant couples are couples in which one partner is living with HIV and the other is HIV-negative. A couple refers to two people in an ongoing sexual relationship; each of these is referred to as a partner in the relationship. How individuals define their relationships varies considerably according to cultural and social context.

Health care services

Continuum of HIV care refers to a comprehensive package of HIV prevention, diagnostic, treatment and support services provided for people living with HIV and their families ranging across: initial HIV diagnosis and linkage to care; management of opportunistic infections and other comorbid conditions; initiating, maintaining and monitoring ART; switching to secondline and third-line ART; and palliative care.

A public health approach addresses the health needs of a population or the collective health status of the people rather than just individuals. A public health approach involves a collaborative effort by all parts of the health sector, working to ensure the well-being of society through comprehensive prevention, treatment, care and support. For HIV, this involves: simplified limited formularies; large-scale use of fixed-dose combinations for first-line treatment for adults and children; care and drugs given free at the point of service delivery, decentralization; and integration of services, including task shifting and simplified clinical and toxicity monitoring.

HIV testing and prevention

Voluntary counselling and testing (also referred to as client-initiated testing and counselling) describes a process initiated by an individual who wants to learn his or her HIV status. Since there are now many different community approaches to providing HIV testing and counselling and people often have mixed motivations for seeking testing (both recommended by a provider and sought by a client), WHO prefers to use the term HIV testing and counselling. All forms of HIV testing and counselling should be voluntary and adhere to the five C’s: consent, confidentiality, counselling, correct test results and connections to care, treatment and prevention services. Quality assurance of both testing and counselling is essential in all approaches to HIV testing and counselling.

Provider-initiated testing and counselling is HIV testing and counselling recommended by a health-care provider in a clinical setting. Provider-initiated testing and counselling, as with all forms of HIV testing and counselling, should be voluntary and adhere to the five C’s.

Combination prevention refers to a combination of behavioural, biomedical and structural approaches to HIV prevention to achieve maximum impact on reducing HIV transmission and acquisition.

ART (antiretroviral therapy)

ARV (antiretroviral) drugs refer to the medicines themselves and not to their use.

ART refers to the use of a combination of three or more ARV drugs to achieve viral suppression. This generally refers to lifelong treatment. Synonyms are combination ART and highly active ART.

ART for prevention is used to describe the HIV prevention benefits of ART.

Eligible for ART refers to people living with HIV for whom ART is indicated according to the definitions of clinical and immunological eligibility in WHO treatment guidelines. The term is often used interchangeably with “needing treatment”, although this implies an immediate risk or an obligation to initiate treatment.

Viral suppression refers to the aim of ART to maintain viral load below the level of detection of available assays, generally less than 50 copies per ml. The current WHO virological criterion for treatment failure is 1000 copies per ml or more.

Universal access to ART is defined broadly as a move to a high level of access (≥80% of the eligible population) for the most effective interventions that are equitable, accessible, affordable, comprehensive and sustainable over the long term; this does not necessarily mean 100% coverage.

Health workforce

Community health workers are health workers who have received standardized and nationally endorsed training outside the nursing, midwifery or medical curricula.

Midwives are people trained to assist in childbirth, including registered and enrolled midwives.

Non-physician clinicians are professional health workers capable of many of the diagnostic and clinical functions of a physician but who are not trained as physicians. These types of health workers are often known as health officers, clinical officers, physician assistants, nurse practitioners or nurse clinicians.

Nurses include professional nurses, enrolled nurses, auxiliary nurses and other nurses such as dental or primary care nurses.


Concentrated HIV epidemic: HIV has spread rapidly in one or more defined subpopulation but is not well established in the general population. Numerical proxy: HIV prevalence is consistently over 5% in at least one defined subpopulation but is less than 1% among pregnant women in urban areas.

Generalized HIV epidemic: HIV is firmly established in the general population. Numerical proxy: HIV prevalence consistently exceeding 1% among pregnant women. Most generalized HIV epidemics are mixed in nature, in which certain (key) subpopulations are disproportionately affected.

Mixed epidemics: people are acquiring HIV infection in one or more subpopulations and in the general population. Mixed epidemics are therefore one or more concentrated epidemics within a generalized epidemic.

Low-level epidemic: epidemics in which the prevalence of HIV infection has not consistently exceeded 1% in the general population nationally or 5% in any subpopulation.

Low-, moderate- and high-uptake ART settings refer to settings in which the uptake of ART among those eligible for ART is less than 50%, 50–80% and greater than 80%, respectively.

A setting with a high burden of TB and HIV refers to settings with adult HIV prevalence ≥1% or HIV prevalence among people with TB ≥5%.

HIV incidence is the number of new people acquiring HIV infection in a given period in a specified population.

HIV prevalence refers to the number of people living with HIV at a specific point in time and is expressed as a percentage of the population.

PMTCT (prevention of mother-to-child transmission of HIV)

In these guidelines, WHO is moving away from the previous terms “Options A, B and B+”. Instead, these guidelines recommend two options: (i) providing lifelong ART to all pregnant and breastfeeding women living with HIV regardless of CD4 count or clinical stage or (ii) providing ART (ARV drugs) for pregnant and breastfeeding women with HIV during the mother-to-child transmission risk period and then continuing lifelong ART for those women eligible for treatment for their own health. In settings that are not implementing lifelong ART for all pregnant and breastfeeding women living with HIV, the distinction between prophylaxis (ARV drugs given for a limited time during the risk period for transmitting HIV from mother to child to prevent this) and treatment (ART given both for the mother’s health, based on current adult eligibility and to prevent vertical transmission) is still important.

ARV drugs for women living with HIV during pregnancy and breastfeeding refers to a triple-drug ARV drug regimen provided to mothers living with HIV primarily as prophylaxis during pregnancy and throughout breastfeeding (when there is breastfeeding) to prevent mother-to-child transmission of HIV. In this option, the mother’s regimen is continued lifelong after delivery or after the breastfeeding ends only if she meets the ART eligibility criteria for her own health based on CD4 count or clinical stage. Previous WHO guidance referred to this as option B.

Lifelong ART for all pregnant and breastfeeding women living with HIV refers to the approach in which all pregnant women living with HIV receive a triple-drug ART regimen regardless of CD4 count or clinical stage, both for their own health and to prevent vertical HIV transmission and for additional HIV prevention benefits. Previous WHO guidance referred to this as option B+.