# HIV and AIDS

HIV care hinges on prompt laboratory diagnosis, immediate linkage to antiretroviral therapy, durable viral suppression, and prevention services for patients and partners. This review focuses on diagnostic interpretation, acute infection, transmission prevention, PrEP, and clinically meaningful immune monitoring.

**Clinical question:** How should clinicians diagnose HIV promptly, link patients to effective ART, and prevent acquisition and onward transmission?

Updated: 2026-08-21T01:20:02.914591+00:00

## What matters in practice
- Start HIV testing with a laboratory HIV-1/HIV-2 antigen-antibody combination assay; use an HIV-1/HIV-2 antibody differentiation assay after a repeatedly reactive result, and obtain HIV RNA when the supplemental antibody assay is negative to identify acute infection.[18]
- Offer effective ART as soon as possible to every person with HIV; viral suppression reduces morbidity, supports near-normal lifespan, and prevents sexual HIV transmission.[18]
- A negative antibody-only home test does not exclude recent infection: the OraQuick In-Home HIV Test has an approximately 3-month window period.[1]
- Promptly refer acute HIV diagnoses for HIV care, screen for other STIs, provide prevention counseling, and consider PEP for exposed partners when the relevant exposure was within 72 hours.[18]
- CD4 count remains clinically relevant for immune status and opportunistic-infection risk; risk rises particularly below 200 cells/µL or CD4 percentage below 14%.[14]
- PrEP is an effective HIV-prevention strategy; CDC has issued guidance for oral PrEP and, in 2025, a clinical recommendation for every-6-month subcutaneous lenacapavir PrEP.[19][23]

## Use the laboratory diagnostic algorithm and actively detect acute infection

Assay selection and discordant-result follow-up determine whether early infection is missed.

For diagnostic testing, CDC recommends beginning with a laboratory-based HIV-1/HIV-2 antigen-antibody combination immunoassay. A repeatedly reactive specimen should undergo a laboratory HIV-1/HIV-2 antibody differentiation assay. This sequence identifies HIV-2 antibodies, a clinically important distinction because HIV-2 monitoring and therapy differ from HIV-1.[18]

If the initial immunoassay is reactive but the supplemental antibody differentiation assay is negative, obtain HIV RNA testing. This discordant pattern can represent acute HIV infection rather than a false-positive screening result.[18]

Acute retroviral syndrome may occur 1 to 6 weeks after acquisition and can include fever, rash, myalgias, headache, or gastrointestinal symptoms. In a patient with compatible illness and recent exposure, a negative or indeterminate antibody-based result should not end the evaluation; obtain virologic testing when acute infection is plausible.[16][18]
- Use laboratory antigen-antibody testing rather than an antibody-only home test when recent exposure or acute infection is a concern.[1][18]
- Interpret a negative oral-fluid OraQuick In-Home HIV Test cautiously after a recent exposure; FDA describes an approximately 3-month window period for this antibody test.[1]
- Counsel that a negative result during a window period does not establish absence of infection or eliminate transmission risk.[1][2]

*HIV diagnostic result sequence and next action.[18]*

| Result pattern | Interpretation requiring action | Next step |
| --- | --- | --- |
| Laboratory HIV-1/HIV-2 antigen-antibody assay nonreactive | Does not exclude very recent infection when exposure timing or acute syndrome is concerning.[1][18] | Reassess exposure timing; use clinician-directed testing options, including virologic testing when acute infection is suspected.[18] |
| Repeatedly reactive antigen-antibody assay | Requires supplemental testing; initial reactivity alone does not establish HIV type.[18] | Order laboratory HIV-1/HIV-2 antibody differentiation assay.[18] |
| Reactive initial assay; negative supplemental antibody assay | Possible acute HIV infection.[18] | Obtain HIV RNA testing.[18] |
| HIV-2 antibody identified | HIV-2 identification is clinically important because monitoring and therapy differ from HIV-1.[18] | Link to HIV-experienced care and select management appropriate to HIV type.[18] |

## Link immediately to care and initiate effective ART

Early diagnosis has direct individual and public-health benefit.

CDC states that effective ART suppressing HIV replication to undetectable levels reduces morbidity, enables near-normal lifespan, and prevents sexual transmission. U.S. Department of Health and Human Services and International Antiviral Society–USA recommendations support offering effective ART as soon as possible to all persons with HIV, both for patient benefit and prevention of transmission.[18]

The supplied evidence supports rapid ART linkage but does not provide regimen-specific dosing, resistance-testing requirements, renal or hepatic selection criteria, drug-interaction management, or laboratory monitoring schedules. Confirm these details in current HHS antiretroviral guidelines and product labeling before prescribing.

For a new acute HIV diagnosis, arrange immediate HIV specialty linkage, screen for STIs, and provide prevention counseling. Counsel patients to reduce partner number and use condoms correctly and consistently while diagnostic evaluation and viral suppression are being established.[18]
- Assess whether sexual or injection-drug-use partners had a potentially transmissible exposure within the preceding 72 hours; discuss PEP availability for partners without known HIV infection.[18]
- Make viral suppression a central treatment and prevention goal because suppression prevents sexual HIV transmission.[18]
- Address barriers to engagement, including social determinants that can impede access to prevention and treatment tools.[24]

*Immediate priorities after HIV diagnosis.[18][24]*

| Priority | Why it changes care | Action |
| --- | --- | --- |
| Rapid linkage to HIV care | Early ART improves health outcomes and reduces HIV transmission.[18] | Arrange prompt HIV clinical care and offer ART as soon as possible.[18] |
| Sexual-transmission prevention | Undetectable HIV replication prevents sexual transmission.[18] | Support treatment initiation and sustained viral suppression.[18] |
| STI evaluation | CDC directs STI screening after an acute HIV diagnosis.[18] | Screen for STIs and manage according to current STI guidance.[18] |
| Partner protection | Partners may be eligible for time-sensitive PEP after recent exposure.[18] | Assess exposure timing; if less than 72 hours, facilitate PEP evaluation.[18] |
| Care access and retention | Nonmedical social determinants affect the effectiveness and reach of HIV prevention and treatment tools.[24] | Identify and address access barriers during linkage and follow-up.[24] |

## Use CD4 count to contextualize opportunistic-infection risk

Viral suppression is the therapeutic objective; CD4 measures residual immune vulnerability.

CD4 count is an important laboratory indicator of immune function and a predictor of disease progression. Opportunistic-infection risk rises as CD4 declines, particularly below 200 cells/µL or when CD4 percentage is below 14%.[11][14]

Profound immunosuppression predicts pathogen-specific vulnerability. Most Pneumocystis jirovecii pneumonia occurs with CD4 counts below 200 cells/µL, whereas cytomegalovirus retinitis typically occurs below 50 cells/µL.[16] These thresholds should prompt review of current opportunistic-infection prophylaxis, diagnostic, and treatment guidance; specific prophylactic regimens are not supplied in the available evidence.

The practical distinction between HIV infection and advanced disease is therefore not merely semantic: immune status changes the differential diagnosis, urgency of symptom evaluation, and need to apply opportunistic-infection prevention guidance. Maintain a low threshold to evaluate compatible pulmonary, neurologic, ocular, constitutional, or mucocutaneous presentations in patients with low CD4 counts.[14][16]
- A CD4 count below 200 cells/µL or CD4 percentage below 14% identifies materially increased opportunistic-infection risk.[14]
- CD4 below 50 cells/µL is associated with risk of CMV retinitis; new visual symptoms warrant urgent assessment.[16]
- Higher CD4 count and undetectable viral load are associated with lower late opportunistic-infection risk in treated patients.[17]

*CD4-associated clinical implications supported by available evidence.[14][16][17]*

| Immune marker | Clinical implication | Practice consequence |
| --- | --- | --- |
| CD4 count below 200 cells/µL or CD4 percentage below 14% | Opportunistic-infection risk increases substantially.[14] | Review current opportunistic-infection prevention guidance and evaluate compatible symptoms urgently.[14] |
| CD4 count below 200 cells/µL | Most Pneumocystis jirovecii pneumonia occurs below this level.[16] | Include Pneumocystis pneumonia prominently in appropriate respiratory evaluations.[16] |
| CD4 count below 50 cells/µL | CMV retinitis typically occurs below this level.[16] | Urgently evaluate compatible visual complaints.[16] |
| Undetectable viral load with higher CD4 count | Associated with lower risk of late opportunistic infections during ART.[17] | Prioritize durable viral suppression and ongoing immune assessment.[17] |

## Match prevention to exposure timing and ongoing risk

PrEP, PEP, testing, and viral suppression are complementary interventions.

PrEP is an evidence-based strategy for people at ongoing risk of HIV acquisition. CDC's 2021 clinical practice guideline provides comprehensive guidance for PrEP in adults and adolescents, and CDC now lists a 2025 clinical recommendation for subcutaneous lenacapavir administered every 6 months for HIV PrEP.[19][23] The supplied excerpts do not provide eligibility criteria, baseline testing, follow-up intervals, or dosing for oral PrEP; consult the current CDC PrEP guidance and FDA labeling for regimen selection and monitoring.

Randomized evidence supports the preventive efficacy of antiretroviral PrEP in women at risk for HIV-1 infection.[8] Adherence is a major determinant of protection with oral PrEP; evidence summarized in a recent trial report notes diminished protection below 40% adherence, although that specific threshold should not substitute for guideline-based adherence assessment or regimen selection.[13]

For a discrete recent exposure, PEP is time sensitive. CDC advises that partners of an individual newly diagnosed with acute HIV should be informed about PEP when their most recent sexual or injection-drug-use contact occurred less than 72 hours earlier.[18]
- Offer prevention assessment at HIV testing encounters, especially after recent STI diagnosis, reported exposure, or ongoing sexual or injection-drug-use risk.[18][23]
- For ongoing risk, discuss PrEP options; CDC lists oral PrEP guidance and injectable lenacapavir PrEP guidance.[19][23]
- For exposure within 72 hours, arrange urgent PEP evaluation rather than waiting for routine follow-up.[18]
- For people living with HIV, sustained viral suppression prevents sexual transmission and should be communicated as a core prevention intervention.[18]

### Pregnancy and infant-feeding counseling

For people with HIV receiving ART with consistent viral suppression during pregnancy, 2023 U.S. guidance recommends counseling about infant-feeding options, including breastfeeding, formula feeding, mixed feeding, and banked donor milk. Available literature suggests transmission risk during breastfeeding with maternal viral suppression is very low but not zero.[7]
- Use shared decision-making and explicitly communicate the residual, nonzero transmission uncertainty described in available evidence.[7]

*Prevention decisions by clinical context.[7][18][19][23]*

| Clinical context | Highest-value action | Evidence limitation in supplied sources |
| --- | --- | --- |
| Ongoing risk of HIV acquisition | Discuss and offer guideline-concordant PrEP; CDC lists oral PrEP guidance and a 2025 recommendation for every-6-month subcutaneous lenacapavir PrEP.[19][23] | Specific eligibility, laboratory testing, and dosing details are not contained in the supplied excerpts. |
| Potential sexual or injection exposure less than 72 hours ago | Facilitate urgent PEP assessment.[18] | Specific PEP regimen and duration are not contained in the supplied excerpts. |
| Patient living with HIV | Initiate effective ART promptly and support durable viral suppression to prevent sexual transmission.[18] | Regimen-specific selection and monitoring details are not contained in the supplied excerpts. |
| Pregnancy with consistent viral suppression on ART | Counsel on breastfeeding, formula, mixed feeding, and banked donor milk; transmission risk with suppression is very low but not zero.[7] | Individual maternal, infant, and feeding-management protocols are not detailed in the supplied excerpts. |

## Common questions

### What should be ordered when the HIV screening assay is reactive but the antibody differentiation assay is negative?

Order HIV RNA testing. CDC identifies this discordant pattern as potentially representing acute HIV infection.[18]

### Can a negative home HIV test exclude infection after a recent exposure?

No. The OraQuick In-Home HIV Test detects HIV-1 and HIV-2 antibodies and has an approximately 3-month window period; a recent exposure requires repeat testing later or clinician-directed testing.[1]

### Does viral suppression prevent sexual HIV transmission?

CDC states that effective ART producing undetectable HIV replication prevents sexual transmission, in addition to reducing morbidity and supporting near-normal lifespan.[18]

### When should partners be assessed for PEP after a new acute HIV diagnosis?

Assess sexual and injection-drug-use partners whose most recent relevant contact was within 72 hours; CDC advises providing information about PEP for partners not known to have HIV infection.[18]

### What CD4 level should heighten concern for opportunistic infections?

Risk rises particularly below 200 cells/µL or a CD4 percentage below 14%. Most Pneumocystis jirovecii pneumonia occurs below 200 cells/µL, and CMV retinitis typically occurs below 50 cells/µL.[14][16]

## References
1. Information regarding the OraQuick In-Home HIV Test | FDA — www.fda.gov — https://www.fda.gov/vaccines-blood-biologics/approved-blood-products/information-regarding-oraquick-home-hiv-test
2. Women and HIV: Get the Facts on HIV Testing, Prevention, ... — www.fda.gov — https://www.fda.gov/consumers/womens-health-topics/women-and-hiv-get-facts-hiv-testing-prevention-and-treatment
3. Barriers and facilitators to HIV pre-exposure prophylaxis for ... — www.thelancet.com — https://www.thelancet.com/journals/lanhiv/article/PIIS2352-3018(23)00080-2/abstract
4. Antiretroviral Drugs for Treatment and Prevention of HIV in ... — jamanetwork.com — https://jamanetwork.com/journals/jama/fullarticle/2827545
5. HIV Screening and Preexposure Prophylaxis Guidelines — jamanetwork.com — https://jamanetwork.com/journals/jama/fullarticle/2735479
6. Antiretroviral Drugs for Treatment and Prevention of HIV ... — jamanetwork.com — https://jamanetwork.com/journals/jama/fullarticle/2799240
7. Risk of transmission of HIV to infants during breast/chest feeding when mothers/birthing parents living with HIV are on antiretroviral therapy: a protocol for a rapid review | BMJ Open — bmjopen.bmj.com — https://bmjopen.bmj.com/content/14/5/e084436
8. results from HPTN 084, a phase 3, randomised clinical trial — www.thelancet.com — https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)00538-4/fulltext
9. Perinatal outcomes associated with pre-exposure ... — www.thelancet.com — https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(24)00111-1/fulltext
10. A Multicentre Prospective and Retrospective Cohort Study — www.thelancet.com — https://www.thelancet.com/journals/lanepe/article/PIIS2666-7762(26)00116-X/fulltext
11. Robustness of viral load over CD4 cell count in measuring the quality of life of people with HIV at second line regimen in Amhara region | Scientific Reports — www.nature.com — https://www.nature.com/articles/s41598-025-93608-y
12. HIV infection | Nature Reviews Disease Primers — www.nature.com — https://www.nature.com/articles/nrdp201535
13. Real-time digital intervention on oral pre-exposure prophylaxis adherence among MSM: randomized controlled trial | npj Digital Medicine — www.nature.com — https://www.nature.com/articles/s41746-025-01743-7
14. Routine CD4 monitoring in HIV patients with viral ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/pii/S1684118217300701
15. Evidence for a diagnostic window in fourth generation assays for HIV — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S1386653201001834
16. Acute HIV Infection - an overview — www.sciencedirect.com — https://www.sciencedirect.com/topics/nursing-and-health-professions/acute-hiv-infection
17. Late-onset opportunistic infections while receiving anti- ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/pii/S1201971222003757
18. HIV - STI Treatment Guidelines — www.cdc.gov — https://www.cdc.gov/std/treatment-guidelines/hiv.htm
19. Guidelines and Recommendations | HIV Nexus — www.cdc.gov — https://www.cdc.gov/hivnexus/hcp/guidelines/index.html
20. HIV Prevention Through Early Detection and Treatment of Other
Sexually Transmitted Diseases -- United States Recommendations of
the Advisory Committee for HIV and STD Prevention — www.cdc.gov — https://www.cdc.gov/mmwr/preview/mmwrhtml/00054174.htm
21. Guidelines and Recommendations | HIV Partners | CDC — www.cdc.gov — https://www.cdc.gov/hivpartners/php/guidelines/index.html
22. HIV PREVENTION IN THE UNITED STATES: New Opportunities, New Expectations — stacks.cdc.gov — https://stacks.cdc.gov/view/cdc/39420/cdc_39420_DS1.pdf
23. Preexposure Prophylaxis for the Prevention of HIV Infection in the United States – 2021 Update: A Clinical Practice Guideline — stacks.cdc.gov — https://stacks.cdc.gov/view/cdc/112360
24. The Role of Housing in Ending the HIV Epidemic — stacks.cdc.gov — https://stacks.cdc.gov/view/cdc/127257/cdc_127257_DS1.pdf

## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.