Understanding HIV: What It Is, How It Spreads, and How It's Treated

In 1981, HIV was a mystery illness killing young people with no clear cause and no treatment. Today, it is a manageable chronic condition. People living with HIV who receive effective treatment can expect near-normal life spans, maintain undetectable viral loads, and — critically — cannot transmit the virus to their partners. The science has transformed HIV from a terminal diagnosis into a treatable disease.

Yet HIV remains a serious public health challenge. More than 40 million people worldwide live with the virus. In the United States, roughly 1.2 million people have HIV — and about 1 in 8 don't know it. Without testing, without treatment, the virus continues to progress, damage the immune system, and claim lives that didn't have to be lost.

"People with HIV who get on and stay on effective treatment can live long, healthy lives and protect their partners." — CDC, About HIV, April 2026

By the Numbers

• 40.8 million people worldwide living with HIV (2024)
• 1.2 million Americans living with HIV
• 39,000 new HIV diagnoses in the U.S. in 2023
• 1 in 8 Americans with HIV don't know their status

What Is HIV — and What Is AIDS?

HIV stands for human immunodeficiency virus. It attacks the body's immune system — specifically CD4 cells (T cells), which are the white blood cells that coordinate the immune response. Over time, without treatment, HIV destroys enough of these cells that the body can no longer fight off infections and diseases.

AIDS — acquired immunodeficiency syndrome — is the most advanced stage of HIV infection. A person is diagnosed with AIDS when their CD4 cell count drops below 200 cells per cubic millimeter of blood (a healthy immune system has 500–1,500), or when they develop one or more "AIDS-defining" opportunistic infections. Not everyone with HIV develops AIDS. With modern antiretroviral therapy, most people with HIV never reach this stage.

HIV and AIDS are not the same thing. HIV is the virus. AIDS is a late-stage condition that develops only when HIV has severely damaged the immune system — and which modern treatment largely prevents. Having HIV does not mean you will develop AIDS.

The Three Stages of HIV Infection

Stage 1 — Acute HIV Infection: Within 2–4 weeks of infection, most people experience flu-like symptoms: fever, fatigue, swollen lymph nodes, sore throat, muscle aches, rash, and headache. Viral load is extremely high at this stage, making it highly infectious. Symptoms typically last a few days to several weeks, then disappear.

Stage 2 — Chronic HIV Infection (Clinical Latency): After acute infection, HIV enters a period of clinical latency. The virus is still active but reproduces at very low levels. Many people have no symptoms at all during this stage, which can last a decade or longer without treatment. People in clinical latency can still transmit HIV.

Stage 3 — AIDS (Advanced HIV Disease): When CD4 cell counts fall below 200, or when opportunistic infections develop, HIV has progressed to AIDS. At this stage, the immune system is severely compromised. AIDS is largely preventable with consistent antiretroviral therapy.

Transmission — and What Does NOT Transmit HIV

HIV is present in blood, semen, vaginal and rectal fluids, breast milk, and pre-seminal fluid. It is transmitted when one of these fluids from a person with HIV enters the bloodstream, mucous membranes, or damaged tissue of another person.

• Sexual contact: The most common route in the U.S. Anal sex carries the highest risk. Vaginal sex also transmits HIV. Using condoms consistently reduces risk significantly.
• Sharing needles or syringes: Sharing injection equipment is a high-risk route for HIV. Never sharing needles and using needle exchange programs dramatically reduces risk.
• Mother to child: HIV can be transmitted during pregnancy, childbirth, or breastfeeding. With proper treatment and care, perinatal transmission rates in the U.S. are below 1%.
• Blood transfusions / occupational: Blood transfusions are now extremely safe due to rigorous screening. Occupational exposure is a low but real risk for healthcare workers.

HIV is NOT transmitted through hugging, shaking hands, coughing, sneezing, saliva, tears, sharing food or drinks, toilet seats, or mosquito bites. HIV cannot be transmitted through casual, everyday contact.

HIV and health equity: In the U.S., Black/African American people account for 38% of new HIV infections despite representing about 12% of the population. Hispanic/Latino people account for 32% of new infections. Gay, bisexual, and other men who have sex with men (MSM) account for 66% of new diagnoses. These disparities reflect structural inequities in access to testing, prevention tools like PrEP, and HIV care.

Prevention Tools That Work

PrEP (Pre-Exposure Prophylaxis): PrEP is medication taken by HIV-negative people that dramatically reduces the risk of acquiring HIV through sex or injection drug use. Daily oral PrEP reduces risk by up to 99%. In a major 2025 breakthrough, the FDA approved injectable lenacapavir (Yeztugo) as PrEP — a twice-yearly injection that showed near-100% efficacy in clinical trials.

PEP (Post-Exposure Prophylaxis): PEP is a 28-day course of antiretroviral medications taken after a potential HIV exposure. It must be started within 72 hours of exposure to be effective. After completing PEP, transitioning to PrEP is strongly advised for ongoing protection.

Condoms: When used consistently and correctly, condoms are highly effective at preventing HIV as well as other sexually transmitted infections.

U=U (Undetectable = Untransmittable): A person with HIV who is on effective treatment and maintains an undetectable viral load cannot sexually transmit HIV to their partner. This is scientifically established and has transformed conversations about HIV prevention, relationships, and stigma.

Know Your Status — Get Tested: The CDC recommends that everyone aged 13–64 get tested for HIV at least once as part of routine health care — and more frequently for those with ongoing risk.

Treatment — Antiretroviral Therapy (ART)

Antiretroviral therapy (ART) is the cornerstone of HIV treatment. ART is a combination of HIV medicines — taken daily — that reduce the amount of HIV in the body (viral load) to undetectable levels. It does not cure HIV, but it controls it so effectively that the immune system recovers and the person can live a near-normal life.

• Start ART as soon as possible after diagnosis: Current guidelines recommend beginning antiretroviral therapy immediately after diagnosis — regardless of CD4 count.
• Achieve viral suppression: The goal of ART is to reduce HIV viral load to undetectable levels. Most people reach undetectable status within 6 months. In 2023, 67% of diagnosed Americans with HIV had achieved viral suppression.
• Stay in care and stay adherent: Consistency is everything. Missing doses allows the virus to replicate and may lead to drug resistance.
• Long-acting injectable ART: For people who struggle with daily oral medication, long-acting injectable ART (cabotegravir + rilpivirine, administered every 1–2 months) is now an approved option.

With treatment, HIV is a manageable chronic condition. People who start ART early, maintain adherence, and stay in care can expect a near-normal life expectancy and cannot transmit HIV to sexual partners.

Get Tested. Get Treated. Get Support.

If you haven't been tested for HIV, the most important thing you can do is find out your status. Testing is fast, confidential, and available at clinics, community health centers, and pharmacies across the country. If you test positive, treatment is available — and the earlier you start, the better the outcome.

If you're HIV-negative and at risk, ask your healthcare provider about PrEP. With the 2025 approval of injectable lenacapavir, there are now more options than ever.

This article is for informational purposes only. Sources: CDC About HIV (April 2026), CDC Fast Facts: HIV in the United States, WHO HIV Data and Statistics (July 2025), UNAIDS 2025, HIV.gov CDC Recommends New Injectable HIV PrEP (September 2025).