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Human immunodeficiency virus infection

Last updated: July 20, 2026

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This article is part of an accredited activity. For full CME information and disclosures, please click on the link in this reference: [1]

Summarytoggle arrow icon

Human immunodeficiency virus (HIV) infection is a chronic viral disease caused by HIV, a retrovirus that targets CD4⁺ T lymphocytes, macrophages, and dendritic cells. Infection with HIV-1 or HIV-2 leads to progressive immune system dysfunction through depletion of CD4⁺ cells and chronic immune activation. Without antiretroviral therapy (ART), the infection typically progresses to acquired immunodeficiency syndrome (AIDS). During the acute infection stage, the virus reproduces rapidly in the body, which can lead to acute, nonspecific (e.g., flu-like) symptoms (acute retroviral syndrome). Approximately half of all infected individuals remain asymptomatic. The next stage is clinical latency, during which individuals may remain asymptomatic or develop non-AIDS-defining conditions (e.g., oral hairy leukoplakia). The last stage, AIDS, is characterized by AIDS-defining conditions (e.g., Kaposi sarcoma) and/or a CD4 count < 200 cells/mm3.

Methods of HIV testing for screening and diagnosis vary by age. Management of confirmed infections includes treatment with ART, monitoring of CD4 count and viral load, management of HIV-associated conditions, and prevention of opportunistic infections. Treatment with ART is indicated throughout pregnancy in individuals with known HIV, and intrapartum IV zidovudine may be used based on viral load to lessen the risk of vertical transmission. HIV prevention in prenatally exposed infants is recommended to prevent acquisition of HIV. In addition to ART, management in children includes additional social support and close monitoring of developmental milestones and pediatric growth parameters.

Partners of HIV-positive individuals and those with other risk factors for HIV infection can reduce the risk of contracting HIV infection by taking HIV pre-exposure prophylaxis or HIV postexposure prophylaxis.

Epidemiologytoggle arrow icon

  • Incidence (in the US)
    • HIV infection: peak incidence between ages 20 and 30 (∼ 35/100,000)
    • AIDS: peak incidence approx. age 45 (∼ 14/100,000)
    • Ethnicity: Incidence is significantly higher in the Black population than in other population groups.
  • Prevalence
    • US: ∼ 1.2 million
    • Global: ∼ 37 million

References:[2][3][4]

Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

Pathogen (human immunodeficiency virus)

  • Family: Retroviridae
  • Genus: Lentivirus
  • Species
    • HIV-1: most common species worldwide
    • HIV-2: restricted almost completely to West Africa
  • Structure: icosahedral with a conical capsid and a spiked envelope
  • Genome
    • Pseudodiploid (2 RNA molecules yielding 1 DNA molecule)
    • 9 genes encoding a total of 15 proteins
  • Function of structural proteins
    • pol gene codes for a polyprotein which consists of
    • gag gene codes for gag protein, which consists of
    • env gene codes for gp160 which gets cleaved into envelope glycoproteins
    • tat gene (trans-activator of transcription) codes for tat protein which promotes viral transcription
    • rev gene: codes for the rev protein, which regulates translocation of unspliced and incompletely spliced mRNAs

Polly is a Really Important Person”: The proteins coded by the pol gene are Reverse transcriptase, Integrase, and Protease.

Routes of HIV transmission [6]

  • Sexual: : accounts for ∼ 80% of infections worldwide
    • Risk per 10,000 exposures [6]
      • Receptive anal intercourse: 138
      • Insertive anal intercourse: 11
      • Receptive vaginal intercourse: 8
      • Insertive vaginal intercourse: 4
      • Receptive or insertive oral intercourse: low risk
    • Modifying factors
      • Viral load: Transmission is unlikely if the viral load is < 200 copies/mL. [7]
      • Reduced risk of infection for circumcised male individuals [8]
      • Genital mucosal damage increases the risk of transmission (e.g., from coinfection with HPV or HSV).
  • Parenteral transmission (risk per 10,000 exposures) [6]
  • Vertical transmission
    • Risk of perinatal HIV transmission: 15–45% without viral suppression; < 1 % with viral suppression [9]
    • Risk of transmission over the course of breastfeeding: up to 20% without viral suppression; < 1% with viral suppression [10][11][12]

Sexual transmission of HIV is preventable if a viral load of < 200 copies/mL is maintained (i.e., undetectable HIV is untransmittable). [7]

Risk factors for HIV infection [13][14]

Pathophysiologytoggle arrow icon

Natural history of HIV infection

Viral load predicts the rate of disease progression and CD4 count correlates with immune function.

Acute HIV syndrome does not develop in all patients. Absence of symptoms may delay diagnosis.

The role of immune response

  • Because HIV infects cells of the immune system itself, activation of cellular immunity is a factor that paradoxically helps the virus spread and ensures chronic persistence of the infection.
  • HIV evades immune control via:
    • Genetic mutation and recombination
    • Downregulation of MHC class I surface molecules in infected cells

References:[3][16][17]

Clinical featurestoggle arrow icon

General considerations

  • There are no clinical features specific to HIV infection
  • In early HIV infection, patients are often asymptomatic.
  • Incubation period: usually 2–4 weeks [18]
  • Infectiousness: two peaks (1st peak: within the first months after infection; 2nd peak: during AIDS-stage)

Acute HIV infection [16]

Clinical latency and AIDS [16]

Test patients with a history of intravenous drug use who present with otherwise unexplained weight loss, depression, and/or dementia for HIV.

Unlike oral candidiasis, esophageal candidiasis is an AIDS-defining condition.

Stagingtoggle arrow icon

CDC classification system for HIV [20]

  • CDC categories of HIV are based on CD4 count in combination with current or previously diagnosed HIV-related conditions.
  • Any patient belonging in categories A3, B3, or C1–C3 is considered to have AIDS.
CD4 cell count category
(normal cell count: 500–1500 cells/mm3)
Clinical category A Asymptomatic, Acute HIV
or PGL
Clinical category B Symptomatic conditions,
not A or C
Clinical category C AIDS-defining conditions
(1) ≥ 500 cells/mm3 A1 B1 C1
(2) 200–499 cells/mm3 A2 B2 C2
(3) < 200 cells/mm3 A3 B3 C3

PGL= Persistent generalized lymphadenopathy

WHO (World Health Organization) classification [21]

WHO classifies individuals with confirmed HIV infection according to clinical features and diagnostic findings:

Screeningtoggle arrow icon

Indications [13][22][23]

Methods [13]

Follow-up [27]

Diagnosistoggle arrow icon

Approach [23][27]

In most US states, HIV testing requires patient consent (opt-out); in the majority of locations, oral consent is sufficient, but check local guidance.

In individuals with a known or potential exposure to HIV and negative testing, repeat testing in 4–6 weeks and 3 months after exposure. [28]

Overview of HIV tests [27]

Serological assays

Serological assays are commonly used for both screening and diagnosis and may detect HIV antigen, antibodies, or both.

Comparison of HIV serological assays [27][29]
Generation Test characteristics
First-generation HIV test
  • Detects IgG only
  • Cannot differentiate between HIV-1 and HIV-2 infection
  • Sensitive but not very specific
Second-generation HIV test
Third-generation HIV test
  • Detects IgG and IgM
  • Cannot differentiate between HIV-1 and HIV-2 infection
  • More sensitive and specific
Fourth-generation HIV test
Fifth-generation HIV test [29]

Virological testing [31][32]

Virological tests are most commonly used for screening infants and confirmation of disease in both infants and adults.

HIV testing

Recommended laboratory-based HIV studies [34][35]
Test purpose Age Preferred test
Initial testing Adults and children ≥ 18 months
Infants < 18 months
Confirmation Adults and children > 24 months
Infants ≤ 24 months

Initial testing for HIV [34]

A negative combination antibody/antigen test two weeks after exposure essentially rules out HIV infection (almost 100% sensitivity).

If the result of a rapid test is positive, a laboratory-based screening test should be sent, followed by confirmatory testing if appropriate. [34]

Confirmatory testing for HIV

Diagnostic testing for patients with newly diagnosed HIV [41][42]

Assessment of organ function

Assessing organ function is important to screen for HIV-associated complications, establish a baseline in order to monitor toxicity, and help select an ART regimen.

Advanced HIV studies

The following studies are recommended to screen for drug resistance, assist in the selection of an appropriate ART regimen, and establish a baseline to monitor the efficacy of therapy.

  • HIV drug resistance testing: Genotypic assays are preferred over phenotypic assays. [41][43]
  • CD4+ count: correlates with overall immune function ; [44]
    • Normal values are > 500 cells/mm3, whereas in the advanced stages of HIV the CD4+ count is often < 200 cells/mm3.
    • Critical measurement to determine when to initiate opportunistic infection prophylaxis
    • CD4+ counts increase in response to successful ART therapy.
  • Viral RNA load: indicator of ART response
    • Decrease in viral loads indicates effective treatment.
    • Prognostic marker in long-term treatment (higher viral load → ↑ destruction of CD4+ lymphocytes more severe immunodeficiency worse prognosis) [45]
  • CD4 cell percentage: used for the assessment of immune function and less variable than CD4+ count [44]
    • Alternative for monitoring children < 5 years of age [46]
    • Values of 14–29% are equivalent to a CD4+ count of 200–500 cells/mm3.
  • CD4:CD8 ratios (no longer routinely recommended): an increase in the ratio following ART initiation suggests improved immune system functioning
  • HLA B*5701 screen: for patients considered for a regimen containing abacavir [42]

Measurement of CD8 cell count and CD4:CD8 ratios is not routinely recommended, as the results are not used to guide treatment. [44]

Managementtoggle arrow icon

General principles [41][47]

Early treatment is particularly critical in patients with a low CD4 count (< 350 cells/mm3), high viral load, or an AIDS-defining illness.

Adherence to ART can be improved by considering social determinants of health and addressing modifiable factors such as comorbid mental illness or substance use disorder, unstable housing, and barriers to attending regular clinic visits. [41]

In the US, HIV/AIDS is a notifiable disease in every state.

Antiretroviral therapytoggle arrow icon

  • Start ART as soon as possible to prevent further progression of the disease. [41]
  • Factors to consider when selecting a regimen include: [41]

Initiation of ART should be delayed in the setting of TB meningitis and cryptococcal meningitis because of the high risk of immune reconstitution syndrome!

Initiation of treatment should not be delayed to await results of advanced HIV studies, e.g., drug resistance or hepatitis screening.

Initial ART regimens [41]

Recommended initial regimens [41]
Regimen Recommended drug combinations Combination tablet Indications/contraindications
2 NRTIs PLUS 1 INI
  • Biktarvy®
  • May be used for immediate treatment in individuals for whom advanced HIV studies are not yet available and whose hepatitis B status is unknown
  • Triumeq®
  • Contraindicated in patients who are HLA-B*5701 positive
1 NRTI PLUS 1 INI
  • Dovato®
  • This regimen should not be given to patients with:

Do not use abacavir-containing regimens for patients with an unknown or positive HLA-B*5701 status, because of the risk of abacavir hypersensitivity reaction!

When available, use combination tablets to reduce pill burden and improve adherence. [48]

Special considerations

See also "HIV in pregnancy" and "HIV in children."

Stopping NRTIs in patients with hepatitis B coinfection can lead to an acute worsening of their hepatitis!

Overview of antiretroviral drugs [41][50][51]

Nucleoside reverse transcriptase inhibitors (NRTIs)


Most NRTIs end in “-ine,” protease inhibitors in “-navir,” and integrase inhibitors in “-gravir.”

“The nuclear plant is in the vuds (read: “woods”)”: Nucleoside reverse transcriptase inhibitors end in “-vudine.”

Nonnucleoside reverse-transcriptase inhibitors (NNRTIs)

HIV protease inhibitors (PIs)

Subtherapeutic doses of ritonavir (boosting agent) can be used to increase concentrations of other HIV drugs because it is a cytochrome P450 inhibitor. [67]

Integrase inhibitors (INIs or InSTIs)

  • Medications in class
    • Bictegravir
    • Cabotegravir
    • Dolutegravir
    • Elvitegravir
    • Raltegravir
  • Mechanism of action: inhibition of the viral integrase → blockade of viral DNA integration into the host's DNA → inhibition of viral replication [50]
  • General adverse effects [53][54]
    • Rash
    • Hypersensitivity syndrome in rare cases
  • Additional medication-specific adverse effects: : muscle inflammation causing elevated creatinine kinase : raltegravir, dolutegravir [53][54]

An intramuscular injection consisting of cabotegravir and rilpivirine can be used for patients whose HIV is well controlled on oral ART but it should not be used as an initial regimen.

Entry inhibitors [68]

Enfuvirtide provides defusion of viral fusion.”

“Maraviroc will block the viral dock.”

Monitoring antiretroviral therapytoggle arrow icon

The treatment response of patients with HIV who are on ART should be frequently monitored by assessing their CD4+ count and HIV viral load. Any concerns regarding the failure of treatment should be referred to the infectious disease service. [41]

Monitoring studies [70]

Frequency of monitoring studies [70]
Frequency of test Test
4–8 weeks after initiation of ART
Every 3–6 months
Every 6 months
Every 12 months

Patients should have monitoring studies performed more frequently if clinically indicated or in treatment failure!

Virological failure [41]

  • Definition: the inability to maintain or achieve viral levels of < 200 copies/mL
  • Causes: patient-related factors (e.g., poor drug adherence, cost), HIV-related factors (e.g., drug resistance, high pretreatment viral load), ART-related factors (e.g., drug interactions, suboptimal pharmacokinetics)
  • Management: Address any identifiable cause of failure and adjust ART regimen if indicated.

Poor CD4 count recovery [41]

  • Definition: CD4+ counts remain persistently low (< 500, although effects are most concerning if CD4 remains < 200) despite adequate suppressive ART. These individuals have increased morbidity and mortality.
  • Causes: medication side effects, coinfections such as HIV-2 and HCV, other medical problems such as malignancy
  • Management: Identify modifiable causes of CD4 cell lymphopenia. Changing or adding antiretrovirals is not recommended.

Preventive health caretoggle arrow icon

Screening tests for individuals with HIV [42]

The purpose of screening is to identify any AIDS-defining illnesses and coinfection with other bloodborne viruses or STIs, and to guide preventive efforts (e.g., vaccinations).

Early detection of coinfections reduces morbidity and prevents onward transmission. Routine testing for HSV IgG, CMV IgG, or inflammatory markers is not recommended. [42]

Immunizations [42][71]

Some live vaccinations (e.g., MMR, varicella, typhoid Ty21a, and yellow fever vaccines) should not be given until the CD4 count is ≥ 200; consult with an infectious diseases specialist before vaccinating patients with low CD4 counts. [71]

The live attenuated influenza vaccine should never be given to HIV patients, regardless of CD4 count.

Malignancy

Risk reduction

Screening [72]

HPV cotesting at the time of a Pap smear is not recommended for patients < 25 years of age because of the high prevalence of infection in this age group, which typically self-resolves. Cotesting may be considered in patients 25–29 years of age with HIV. [72]

Complicationstoggle arrow icon

Patients who start ART are at risk of developing complications related to the recovery of their immune system. Complications relating to immunocompromise (especially if CD4 levels are < 200) and/or HIV infection itself (e.g., chronic immune activation and inflammation) may also be seen (see “HIV-associated conditions).

Immune reconstitution inflammatory syndrome (IRIS) [73][74]

  • Definition: an inflammatory syndrome that can occur after initiation of ART and consists of either the appearance of a new condition or worsening of a preexisting condition
  • Epidemiology: common; occurs in ∼ 15–25% of patients starting ART [75]
  • Etiology: believed to result from the restoration of the immune system and its response to antigenic stimulation. The stimulus may be: [73]
  • Risk factors [73]
  • Clinical presentation [74]
    • Develops within 4–8 weeks of initiation of ART
    • Presentation varies depending on the underlying illness, however, patients often have clinical deterioration and localized tissue inflammation.
  • Diagnosis is clinical and based on presence of the following: : [76]
    • Symptoms cannot be explained by the expected clinical course of a known infection, a drug side-effect, or a new infection.
    • Symptoms of an infectious or inflammatory (e.g., autoimmune) condition
    • Treatment with effective ART (defined by a significant decrease in HIV viral RNA or an increase in CD4 count)
    • HIV diagnosis
  • Management [74]
  • Prevention

Corticosteroids should not be given to prevent IRIS, nor should they be used to manage IRIS caused by Kaposi sarcoma or cryptococcal meningitis! [74]

We list the most important complications. The selection is not exhaustive.

Prognosistoggle arrow icon

  • Morbidity and mortality among patient subsets
    • Untreated, HIV leads to death on average 8–10 years after infection.
    • Progression varies among individuals: Some patients may die within a few years while others can remain asymptomatic for decades.
      • Untreated individuals with advanced HIV infection usually die within a few years (median survival is 12–18 months).
        • Some untreated individuals show only slow progression and can remain asymptomatic for more than 20 years.
        • In rare cases, untreated individuals have no detectable viremia and continue to have high CD4 counts for long periods.
    • The average life expectancy of HIV-infected individuals who receive adequate antiretroviral treatment is approaching that of noninfected individuals of the same age. [77][78]
    • Individuals with HIV infection on adequate antiretroviral therapy are more likely to develop chronic comorbidities (e.g., cardiovascular disease, diabetes, cancer) than healthy individuals. [79][80]
  • Individual prognosis depends on various factors, including:
    • Adequate antiretroviral treatment
    • Viral set point; and CD4 count
    • Exposure to opportunistic pathogens
    • Individual genetic properties
    • HIV species and subtype
    • Preexisting conditions

Preventiontoggle arrow icon

Risk reduction [81]

All patients should be counseled on the following risk reduction measures.

HIV pre-exposure prophylaxis (PrEP) [82][83]

Acute HIV infection should always be ruled out in patients starting PrEP since a two-drug regimen can lead to resistant mutations in patients who already have HIV.

HIV postexposure prophylaxis (PEP) [28][87]

Special patient groupstoggle arrow icon

The approach to HIV infection requires additional considerations in pregnant individuals and children.

HIV in pregnancytoggle arrow icon

The etiology of HIV and clinical features of HIV are the same as in nonpregnant adults.

HIV screening in pregnancy [12][88]

Antenatal screening

Intrapartum screening

Diagnosis of HIV in pregnancy [12][88]

Diagnosis of HIV infection is the same as in nonpregnant adults.

Management of HIV in pregnancy [12][89] [90]

Management of HIV in pregnancy is typically performed by specialists (e.g., MFM, infectious diseases).

Prenatal management [9][12][89]

ART that maintains a viral load of < 50 copies/mL from conception through delivery effectively eliminates the risk of vertical transmission. [12][42]

Intrapartum management [90]

Intrapartum management of HIV is based on viral load and adherence to ART. [12][90]

Intrapartum management of HIV [12][89][90]
Viral load Delivery considerations Intrapartum ART
  • Maternal viral load: > 1000 copies/mL (highest risk)
  • Maternal viral load: 50–1000 copies/mL
  • Maternal viral load: < 50 copies/mL
  • IV zidovudine is not recommended.
  • All patients receiving ART: Continue regular regimen.

Consult a specialist for guidance on the mode of delivery for individuals with an unknown viral load or concerns about ART adherence.

Avoid fetal scalp electrodes during delivery in the setting of maternal HIV, especially when maternal viral load is ≥ 50 copies/mL. [12]

The National Clinical Consultation Center (844-275-6222) is available 24/7 for individualized clinical guidance on perinatal HIV and AIDS. [12][90]

Postpartum management [12][89][90]

Postpartum management of HIV requires a multidisciplinary care team (e.g., physicians, social workers, and patient advocates).

HIV in childrentoggle arrow icon

Etiology [42][92]

Clinical features of HIV in children [42][93]

Infants and young children [42][93]

The clinical features of untreated HIV are nonspecific and include:

Adolescents [31][95]

Diagnosis [31][97]

HIV infection is a nationally notifiable disease in the US. Notify state and local public health authorities if diagnosis is confirmed. [97]

Be aware of state laws regarding confidentiality for HIV care in minors. [98]

Management of confirmed HIV infection in children [31][42][97]

Most live vaccines (e.g., MMR, varicella) are contraindicated in children with CD4 < 15% or CD4 < 200 cells/mm³. [92][93][94]

Rapid ART initiation is vital for children, particularly infants, to prevent disease progression and sequelae (e.g., neurodevelopmental disorders, cardiopulmonary disease, immunocompromise). [42]

Management of infants with perinatal HIV exposure [31]

Virological testing (HIV NAT)

  • Testing frequency
    • At birth
    • At 14–21 days
    • At 1–2 months
    • At 2–3 months in selected infants [31]
    • At 4–6 months
  • Follow-up
    • Positive virological test: Confirm diagnosis with a second virological test.
    • Breastfed infants
    • Non-breastfed infants: Perinatal HIV infection can be excluded in infants meeting the criteria below. [31]
      • ≥ 2 negative virologic tests, with one negative test obtained at ≥ 1 month and at ≥ 4 months of age
      • OR 2 negative HIV antibody tests from separate specimens obtained at ≥ 6 months of age [31]

ART for infant HIV prophylaxis [31]

If breastfeeding, additional prophylaxis may be recommended. [31]

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