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Epidemiology of HIV Infection

Q: Which populations are classified as high-risk groups for HIV infection?

Vulnerable and high-risk groups include: People who inject drugs (PWID) — due to unsterilized equipment.Commercial sex workers — due to multiple sexual partners.Men who have sex with men (MSM) — a significantly affected vulnerable group.Individuals with high-risk or multiple sexual partnerships.Regular sexual partners of HIV-positive individuals.Inmates — populations in correctional facilities.Migrants and mobile populations.Healthcare workers — vulnerable due to potential occupational exposure via needlesticks or sharps injuries.

Human immunodeficiency virus

For medical students2 min readUpdated 2026-10-10

The epidemiology of HIV infection describes a massive pandemic currently spanning all continents. The modern epidemic process is characterized by a paradoxical increase in the pool of infected individuals, driven both by the continuous emergence of new cases and by the increased life expectancy of patients.

Pandemic geographyThe infection is widespread globally, encompassing every continent on Earth.

Viral epicentersEast Africa for HIV-1 and West Africa for HIV-2.

High-risk demographicYoung adults aged 15 to 24 account for a significant proportion of newly diagnosed individuals.

Frequent transmission routeSexual contact between men accounts for a substantial percentage of transmissions.

Global Distribution and Statistics

HIV infection is a pandemic affecting all continents without exception. Historically, two main geographic epicenters for different types of the virus have emerged:

HIV-1 originated and circulates most widely in East Africa.
HIV-2 is predominantly localized and spreads within West Africa.

According to historical World Health Organization data, the global burden of the problem was estimated at over 40 million infected individuals worldwide, with cumulative deaths exceeding 3 million.

Demographically, a notable epidemiological feature is the age distribution of virus carriers: a substantial proportion of infected individuals worldwide consists of young adults aged 15 to 24 years, highlighting the high vulnerability of youth to the epidemic process.

Dynamics of Incidence and Causes of Growth

Data analysis demonstrates that an increase in the number of individuals infected with the human immunodeficiency virus is continuously observed in both developing and economically developed regions of the world, including North America and Western Europe.

The increase in the total number of patients living with HIV is driven by two fundamental factors:

Widespread use of antiretroviral therapy (ART). Modern treatment effectively suppresses viral replication and significantly prolongs patients' lives. As a result, mortality decreases, and the total pool of infected individuals living with the virus naturally increases.
Emergence of new infections. Despite preventive measures, transmission of the virus to uninfected individuals continues, constantly replenishing the reservoir of infection.

Transmission Routes and Mechanisms

Human immunodeficiency virus is characterized by mechanisms of transmission typical of classic blood-borne and mucosal infections.

Main transmission routes:

Sexual route. This is the dominant mechanism. Transmission occurs through both heterosexual and homosexual contacts, with unprotected sexual intercourse accounting for a major share of global cases.
Parenteral (hematogenous) route. Driven by direct entry of the virus into the bloodstream. This category includes intravenous drug use involving unsterilized equipment. Transmission is also possible via transfusion of infected blood and blood products, transplantation of donor organs and tissues, and the use of non-sterile medical instruments (posing occupational risks to healthcare workers).
Vertical route. Represents transmission from an infected mother to her child. This process can occur at three stages: during pregnancy (in utero), directly during labor and delivery, and in the postpartum period via breastfeeding.

Mnemonic

To remember the transmission routes, use the mnemonic SPV: Sexual, Parenteral (hematogenous), Vertical.

Frequently asked questions

In which biological body fluids is the HIV concentration sufficient for transmission?

A high concentration of the virus, sufficient for transmission, is found in blood, semen, and vaginal secretions.

Body fluids with low (negligible) concentrations of HIV include breast milk, saliva, tears, and urine. However, breast milk, despite a lower viral concentration, remains an important vehicle for vertical transmission from mother to child.

Which immune system cells are the primary targets for HIV?

The primary targets for the virus are immune cells bearing the CD4 surface receptor and chemokine coreceptors (such as CCR5 and CXCR4).

These include:

T helper cells (Th lymphocytes) — immunoregulatory lymphocytes that are depleted during viral interaction.
Macrophages — including alveolar macrophages of the lungs.
Monocytes — acting as viral reservoirs in the body.
Dendritic cells — follicular dendritic cells and Langerhans cells.
Eosinophils — which also express CD4 receptors.

Which populations are classified as high-risk groups for HIV infection?

Vulnerable and high-risk groups include:

People who inject drugs (PWID) — due to unsterilized equipment.
Commercial sex workers — due to multiple sexual partners.
Men who have sex with men (MSM) — a significantly affected vulnerable group.
Individuals with high-risk or multiple sexual partnerships.
Regular sexual partners of HIV-positive individuals.
Inmates — populations in correctional facilities.
Migrants and mobile populations.
Healthcare workers — vulnerable due to potential occupational exposure via needlesticks or sharps injuries.

What are the clinical stages of HIV infection?

Standard clinical staging typically outlines the progression of the disease through key phases:

Stage 1 — Acute infection / incubation period.
Stage 2 — Primary manifestations (asymptomatic, acute syndrome without secondary conditions, and acute syndrome with secondary conditions).
Stage 3 — Latent (subclinical) stage.
Stage 4 — Secondary diseases (opportunistic infections and neoplasms of varying severity).
Stage 5 — Terminal stage.

What structural genes make up the HIV genome?

The HIV genome contains three primary structural genes encoding major precursor polyproteins:

gag (group-specific antigen) — encodes core structural proteins, including the capsid, nucleocapsid, and matrix proteins.
pol (polymerase) — encodes essential viral enzymes required for replication (reverse transcriptase, integrase, protease, and RNase H).
env (envelope) — encodes envelope glycoproteins (surface glycoprotein gp120 and transmembrane glycoprotein gp41).

Why does the number of people living with HIV continue to grow in developed countries?

The increase in infected individuals in developed countries is driven not only by new infections but also by the widespread use of antiretroviral therapy (ART), which extends patients' lives and thereby expands the total pool of carriers.

What are the geographic epicenters for different types of HIV?

The geographic epicenter for HIV-1 is East Africa, whereas HIV-2 is most prevalent in West Africa.

What is the primary mode of HIV transmission according to statistics?

Statistically, the highest percentage of infections occurs via the sexual route, including both homosexual and unprotected heterosexual contacts.

What is a key age-related feature of the HIV epidemic?

A critical epidemiological feature is that a high proportion of individuals acquiring the infection fall into the young adult category, specifically ages 15 to 24.

Go deeper

Impact of antiretroviral therapy on epidemiological indicators
Occupational risks and prevention of hematogenous transmission in healthcare
Mechanisms of vertical HIV transmission and preventive interventions
Analysis of transmission dynamics across different social groups