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PubMed This is a summary of 22 peer-reviewed journal articles Updated
Human Immunodeficiency Virus Infection

Understanding Your Diagnosis: HIV and AIDS

At a Glance

AIDS is the most advanced stage of HIV infection, marked by a CD4 count below 200, a CD4 percentage below 14%, or an AIDS-defining illness. HIV treatment can restore immune function, and an undetectable viral load maintained for at least six months means U=U: effectively no sexual transmission risk.

Receiving a diagnosis of HIV (Human Immunodeficiency Virus) can feel overwhelming, especially if the word AIDS (Acquired Immunodeficiency Syndrome) is mentioned. It is important to understand that these two terms are not the same. HIV is the virus that causes the infection, while AIDS is the most advanced stage of that infection [1][2]. Today, with modern medical care, a diagnosis of AIDS is not a final sentence; it is a clinical marker that helps your doctors determine the level of care your immune system needs [3][4].

How HIV Affects Your Body

HIV works by targeting and entering specific cells in your immune system called CD4+ T-cells (often just called CD4 cells or “T-cells”). These cells are the “generals” of your immune system, responsible for coordinating your body’s defense against infections [5].

The virus attaches to the CD4 cell, enters it, and integrates its own genetic material into the cell’s DNA [5]. Once inside, it turns the cell into a factory to produce more virus. This process destroys the CD4 cells in several ways:

  • Direct Infection: The virus kills the cells it infects [5].
  • Pyroptosis: This is a type of “cell suicide.” When HIV tries to infect a cell but doesn’t quite succeed, it can trigger a severe inflammatory response that causes the cell to rupture and die [6].
  • Immune Activation: Because your body is constantly trying to fight the virus, your immune system remains in a state of “high alert.” This chronic immune activation (long-term inflammation) can wear down your immune system over time [7][8].

Defining HIV Stages and AIDS

Doctors use a staging system developed by the CDC to track the progression of the virus. For adults and adolescents, the stages are primarily based on your CD4 count (the number of CD4 cells in a microliter of blood), your CD4 percentage, or the presence of specific illnesses [9][1].

  • Stage 1: Your immune system is still strong, with a CD4 count of 500 cells/µL or higher, or a CD4 percentage of 26% or more [9].
  • Stage 2: The immune system is showing signs of weakening, with a CD4 count between 200 and 499 cells/µL, or a CD4 percentage of 14% to 25% [9].
  • Stage 3 (AIDS): This is the most advanced stage. You are diagnosed with AIDS if you meet any of these criteria:
    1. Your CD4 count drops below 200 cells/µL [9][10].
    2. Your CD4 percentage drops below 14% [9].
    3. You develop an AIDS-defining illness, which is a specific type of infection or cancer that typically only occurs in people with severely weakened immune systems [11][2].

Examples of AIDS-defining illnesses include certain types of pneumonia (Pneumocystis jirovecii), widespread fungal infections, or specific cancers like Kaposi sarcoma [12][13]. Even if your CD4 count is above 200, having one of these illnesses will result in a Stage 3 diagnosis [11].

The Path to Recovery

The most critical thing to know about an AIDS diagnosis today is that your immune function can recover substantially [3]. Antiretroviral Therapy (ART)—the standard treatment for HIV—stops the virus from replicating. When the virus is controlled, your immune system has the chance to repair itself.

Many people who are diagnosed with AIDS see their CD4 counts rise back into the healthy range (Stage 1 or 2) after starting treatment [14][15]. While a history of an AIDS-defining illness or a prior Stage 3 diagnosis remains an important part of your clinical record, the immediate immune risk is reduced [3][4]. Early diagnosis and starting ART immediately are the best ways to ensure a long, healthy life [16][17].

Understanding U=U

A major breakthrough in HIV care is the concept of U=U, which stands for Undetectable = Untransmittable.

When you take your ART consistently and your viral load (the amount of HIV in your blood) becomes so low that a standard lab test cannot detect it (generally below 200 copies/mL), you are considered “undetectable” [18]. Extensive clinical studies have proven that people with a maintained undetectable viral load for at least six months have effectively zero risk of passing HIV to their sexual partners [19][20].

This means that by managing your own health through treatment, you are also protecting others. U=U applies to sexual transmission; it does not prevent other STIs or pregnancy and does not establish zero risk for sharing injection equipment or breastfeeding. It requires ongoing monitoring, and you should always contact your care team if your viral load rebounds. U=U is a powerful tool for reducing the stigma around HIV and allowing people living with the virus to have healthy, fulfilling relationships without the fear of sexual transmission [21][22].

Common questions in this guide

What is the difference between HIV and AIDS?
HIV is the virus that causes the infection, while AIDS is the most advanced stage of HIV infection. A person can have HIV without having AIDS, and effective treatment can prevent or delay progression to AIDS.
How do doctors determine whether HIV has reached AIDS?
AIDS, also called Stage 3 HIV infection, is diagnosed if the CD4 count is below 200 cells/µL, the CD4 percentage is below 14%, or an AIDS-defining illness is present. An AIDS-defining illness can qualify even when the CD4 count is above 200.
Can my immune system recover after an AIDS diagnosis?
Yes. Antiretroviral therapy stops HIV from making more copies, allowing CD4 cells and immune function to recover substantially in many people. A previous AIDS diagnosis or AIDS-defining illness remains part of the medical record even when CD4 results improve.
What does U=U mean for someone living with HIV?
U=U means Undetectable = Untransmittable. When treatment keeps the viral load below the level detected by standard testing—generally under 200 copies/mL—for at least six months, studies show effectively zero risk of sexual transmission to partners. U=U does not prevent other STIs or pregnancy and does not remove risks related to shared injection equipment or breastfeeding.
What do my CD4 count and CD4 percentage tell me?
The CD4 count measures the number of CD4 cells in a microliter of blood, and the CD4 percentage is another measure of your immune status. Doctors use both results, along with certain illnesses, to stage HIV and assess how much immune support you may need. Your care team can explain what your results mean over time.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is my current CD4 count and CD4 percentage, and what stage of HIV does that indicate?
  2. 2.Do I have any symptoms or test results that qualify as an AIDS-defining illness?
  3. 3.Given my current results, how often will we monitor my viral load and CD4 count?
  4. 4.If I have reached Stage 3 (AIDS), what are the specific steps we will take to help my immune system recover?
  5. 5.Based on my viral load, am I at the point where 'Undetectable = Untransmittable' (U=U) applies to me?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (22)
  1. 1

    AIDS-related opportunistic illnesses and early initiation of HIV care remain critical in the contemporary HAART era: a retrospective cohort study in Taiwan.

    Lee CY, Tseng YT, Lin WR, et al.

    BMC infectious diseases 2018; (18(1)):352 doi:10.1186/s12879-018-3251-1.

    PMID: 30055564
  2. 2

    The Epidemiology of HIV Among People Born Outside the United States, 2010-2017.

    Kerani RP, Satcher Johnson A, Buskin SE, et al.

    Public health reports (Washington, D.C. : 1974) 2020; (135(5)):611-620 doi:10.1177/0033354920942623.

    PMID: 32805191
  3. 3

    Effects of Antiretroviral Therapy on CD4+ Cell Count, HIV Viral Load and Death in a South African Cohort: A Modelling Study.

    Shoko C, Chikobvu D, Bessong PO

    Pakistan journal of biological sciences : PJBS 2020; (23(4)):542-551 doi:10.3923/pjbs.2020.542.551.

    PMID: 32363840
  4. 4

    Long-term Outcomes of Cytomegalovirus Retinitis in the Era of Modern Antiretroviral Therapy: Results from a United States Cohort.

    Jabs DA, Ahuja A, Van Natta ML, et al.

    Ophthalmology 2015; (122(7)):1452-63.

    PMID: 25892019
  5. 5

    CCR5 as a Coreceptor for Human Immunodeficiency Virus and Simian Immunodeficiency Viruses: A Prototypic Love-Hate Affair.

    Jasinska AJ, Pandrea I, Apetrei C

    Frontiers in immunology 2022; (13()):835994 doi:10.3389/fimmu.2022.835994.

    PMID: 35154162
  6. 6

    Blood-Derived CD4 T Cells Naturally Resist Pyroptosis during Abortive HIV-1 Infection.

    Muñoz-Arias I, Doitsh G, Yang Z, et al.

    Cell host & microbe 2015; (18(4)):463-70.

    PMID: 26468749
  7. 7

    T-Cell Activation Independently Associates With Immune Senescence in HIV-Infected Recipients of Long-term Antiretroviral Treatment.

    Cobos Jiménez V, Wit FW, Joerink M, et al.

    The Journal of infectious diseases 2016; (214(2)):216-25 doi:10.1093/infdis/jiw146.

    PMID: 27073222
  8. 8

    HIV-1-Host Interaction in Gut-Associated Lymphoid Tissue (GALT): Effects on Local Environment and Comorbidities.

    Moretti S, Schietroma I, Sberna G, et al.

    International journal of molecular sciences 2023; (24(15)) doi:10.3390/ijms241512193.

    PMID: 37569570
  9. 9

    Trends in Time From HIV Diagnosis to First Viral Suppression Following Revised US HIV Treatment Guidelines, 2012-2017.

    Crepaz N, Song R, Lyss S, Hall HI

    Journal of acquired immune deficiency syndromes (1999) 2020; (85(1)):46-50 doi:10.1097/QAI.0000000000002398.

    PMID: 32379083
  10. 10

    Prevalence of advanced HIV disease in sub-Saharan Africa: a multi-country analysis of nationally representative household surveys.

    Stelzle D, Rangaraj A, Jarvis JN, et al.

    The Lancet. Global health 2025; (13(3)):e437-e446 doi:10.1016/S2214-109X(24)00538-2.

    PMID: 40021302
  11. 11

    Late presentation among patients with human immunodeficiency virus infection in Turkey.

    Karaosmanoğlu HK, Mete B, Gündüz A, et al.

    Central European journal of public health 2019; (27(3)):229-234 doi:10.21101/cejph.a5416.

    PMID: 31580559
  12. 12

    The late-presenting HIV-infected patient 30 years after the introduction of HIV testing: spectrum of opportunistic diseases and missed opportunities for early diagnosis.

    Tominski D, Katchanov J, Driesch D, et al.

    HIV medicine 2017; (18(2)):125-132 doi:10.1111/hiv.12403.

    PMID: 27478058
  13. 13

    Review of cytomegalovirus coinfection in HIV-infected individuals in Africa.

    Grønborg HL, Jespersen S, Hønge BL, et al.

    Reviews in medical virology 2017; (27(1)) doi:10.1002/rmv.1907.

    PMID: 27714898
  14. 14

    Five-Year Immune Recovery After ART Initiation Among PLWH Aged ≥15 Years with Baseline Immunosuppression - China, 2013-2024.

    Geng Y, Jia H, Guan Y, et al.

    China CDC weekly 2026; (8(25)):772-779 doi:10.46234/ccdcw2026.125.

    PMID: 42433220
  15. 15

    Determinants of suboptimal immune recovery among a Chinese Yi ethnicity population with sustained HIV suppression.

    Chen L, Liu CH, Kang S, et al.

    BMC infectious diseases 2022; (22(1)):137 doi:10.1186/s12879-022-07113-y.

    PMID: 35135485
  16. 16

    HIV infection/AIDS.

    Tsukada K

    Nihon rinsho. Japanese journal of clinical medicine 2016; (74(12)):1992-1997.

    PMID: 30550655
  17. 17

    Initiation of Antiretroviral Therapy in Early Asymptomatic HIV Infection.

    , Lundgren JD, Babiker AG, et al.

    The New England journal of medicine 2015; (373(9)):795-807 doi:10.1056/NEJMoa1506816.

    PMID: 26192873
  18. 18

    Progress with Scale-Up of HIV Viral Load Monitoring - Seven Sub-Saharan African Countries, January 2015-June 2016.

    Lecher S, Williams J, Fonjungo PN, et al.

    MMWR. Morbidity and mortality weekly report 2016; (65(47)):1332-1335 doi:10.15585/mmwr.mm6547a2.

    PMID: 27906910
  19. 19

    Sexual Activity Without Condoms and Risk of HIV Transmission in Serodifferent Couples When the HIV-Positive Partner Is Using Suppressive Antiretroviral Therapy.

    Rodger AJ, Cambiano V, Bruun T, et al.

    JAMA 2016; (316(2)):171-81 doi:10.1001/jama.2016.5148.

    PMID: 27404185
  20. 20

    Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER): final results of a multicentre, prospective, observational study.

    Rodger AJ, Cambiano V, Bruun T, et al.

    Lancet (London, England) 2019; (393(10189)):2428-2438 doi:10.1016/S0140-6736(19)30418-0.

    PMID: 31056293
  21. 21

    HIV infection.

    Deeks SG, Overbaugh J, Phillips A, Buchbinder S

    Nature reviews. Disease primers 2015; (1()):15035 doi:10.1038/nrdp.2015.35.

    PMID: 27188527
  22. 22

    Antiretroviral Therapy for the Prevention of HIV-1 Transmission.

    Cohen MS, Chen YQ, McCauley M, et al.

    The New England journal of medicine 2016; (375(9)):830-9 doi:10.1056/NEJMoa1600693.

    PMID: 27424812

This page explains HIV stages, AIDS, CD4 results, and U=U for informational purposes only and does not constitute medical advice. Discuss your results and treatment plan with your HIV care team.

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