HIV infection and AIDS !

HIV is a virus that slowly destroys the immune system's CD4 cells; without treatment it progresses to AIDS, with serious infections and some cancers.

Updated 2026-10-30

Structures involved

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In biochemistry

Microorganisms that cause it

In immunology

In the clinical exam

Lymph node examination

In physiology

Why it happens

What it is

A chronic infection by the human immunodeficiency virus, which destroys CD4 T lymphocytes; without treatment it progresses to AIDS, with opportunistic infections and certain cancers.

Who gets it

Present in every country; in Latin America it is concentrated in key populations such as men who have sex with men, transgender women and sex workers, with many people diagnosed late. A 2018 meta-analysis (53 studies, 22,603 people, 25 Latin American and Caribbean countries) estimated optimal adherence to antiretroviral therapy at only 70%.

Causes

HIV-1 (most infections worldwide) and HIV-2
Sexual transmission (anal, vaginal)
Sharing needles or syringes
Mother-to-child transmission in pregnancy, delivery or breastfeeding
Blood or blood products (rare where blood is screened); needlestick injury

Risk factors

Condomless sex, multiple partners
Other sexually transmitted infections
Injecting drug use
Partner with HIV who is not virally suppressed
No access to testing or pre-exposure prophylaxis

Pathophysiology

HIV binds CD4 and a co-receptor, copies its RNA into DNA with reverse transcriptase and integrates into the host genome. Ongoing replication, mainly in lymphoid tissue and gut, depletes CD4 cells and causes chronic immune activation. As CD4 counts fall, the risk of opportunistic infections and cancers rises.

Classification

Acute (primary) HIV infection
Chronic asymptomatic infection
Symptomatic infection
AIDS: CD4 count below 200 cells/µL or an AIDS-defining illness (commonly used definition)

Symptoms and signs

Acute infection: fever, sore throat, rash, swollen lymph nodes, flu-like illness
Long silent phase without symptoms
Persistent generalized lymphadenopathy
Weight loss, night sweats, chronic diarrhea
Oral thrush or hairy leukoplakia
Recurrent or severe infections, shingles

Diagnosis

Clinical: Testing is offered routinely and whenever there is a risk exposure, a sexually transmitted infection, tuberculosis or an indicator illness.
Tests: Fourth-generation antigen/antibody test with confirmation by national algorithm; rapid tests for screening. Baseline CD4 count, HIV viral load, resistance testing, and screening for hepatitis B and C, syphilis and tuberculosis.
Imaging: Guided by complications: chest X-ray for pneumonia or tuberculosis, brain CT or MRI for neurological signs.

Differential diagnosis

Infectious mononucleosis (in acute HIV)
Tuberculosis
Lymphoma
Other causes of immunodeficiency
Secondary syphilis

Goal of treatment

Suppress the virus to undetectable levels for life, restore CD4 counts and immune function, prevent opportunistic infections, and stop transmission.

Treatment

Medical: Antiretroviral therapy (ART) for everyone diagnosed, started early: a combination of drug classes (nucleoside reverse transcriptase inhibitors with an integrase inhibitor, or alternatives).
Medical: Prophylaxis against opportunistic infections, such as trimethoprim-sulfamethoxazole when the CD4 count is low, and preventive treatment for latent tuberculosis.
Follow-up: Regular viral load and CD4 counts to confirm suppression, check adherence and detect resistance.
Lifestyle: Adherence support, vaccinations, and care for mental health and substance use.

Drugs for this condition

Complications

Pneumocystis pneumonia
Tuberculosis (pulmonary and extrapulmonary)
Cerebral toxoplasmosis and cryptococcal meningitis
Cytomegalovirus retinitis
Oral and esophageal candidiasis
Kaposi sarcoma and lymphomas
Immune reconstitution inflammatory syndrome after starting ART

Prognosis

With early, sustained ART, life expectancy approaches that of the general population. A person with an undetectable viral load does not transmit HIV sexually (U=U). Untreated, most progress to AIDS over years.

Prevention

Condoms
Pre-exposure (PrEP) and post-exposure (PEP) prophylaxis
Treatment of people with HIV to an undetectable viral load
Testing in pregnancy and prevention of mother-to-child transmission
Sterile injecting equipment and screened blood

Test yourself

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What do the CD4 count and the viral load each tell the clinician?

The CD4 count measures immune status and the risk of opportunistic infections; the viral load measures HIV replication and whether ART is working.

Which CD4 count threshold is commonly used to define AIDS?

A CD4 count below 200 cells/µL, or the presence of an AIDS-defining illness, regardless of the count.

What does «U=U» mean?

Undetectable = untransmittable: a person with HIV who keeps an undetectable viral load on ART does not transmit HIV through sex.

Which opportunistic infection typically causes dry cough, breathlessness and hypoxemia with low CD4?

Pneumocystis jirovecii pneumonia.

Why is tuberculosis screening essential in people with HIV?

HIV greatly increases the risk of active tuberculosis, which is a leading cause of death in people with HIV; latent TB can be treated preventively.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: HIV and AIDS (StatPearls (NCBI Bookshelf), 2026); Adherence to antiretroviral therapy for HIV/AIDS in Latin America and the Caribbean: Systematic review and meta-analysis (Journal of the International AIDS Society, 2018) · adapted, CC BY 4.0.

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Representative model, for educational purposes only.

Neck lymph nodes highlighted on the Durgical 3D model