About Human Immunodeficiency Virus (HIV)
Human immunodeficiency virus (HIV) attacks the immune system, especially CD4 T cells. Without treatment, HIV can progressively weaken immunity and may advance to acquired immunodeficiency syndrome (AIDS), the most advanced stage of HIV infection. HIV is manageable with effective treatment, and people who start and continue treatment can live long, healthy lives.
HIV can be transmitted when certain body fluids—blood, semen and pre-seminal fluid, vaginal or rectal fluids, or breast milk—from a person with HIV enter another person’s bloodstream or contact a mucous membrane or damaged tissue. The main routes are:
- Anal or vaginal sex without an effective prevention method
- Sharing needles, syringes, or other injection equipment
- Transmission during pregnancy, childbirth, or breastfeeding
- Rarely, occupational exposure or transfusion with unscreened blood
HIV is not spread through air, water, saliva, sweat, tears, insects, toilet seats, or ordinary contact such as hugging, shaking hands, or sharing dishes. Oral sex carries little to no risk in most circumstances. A person with HIV who takes antiretroviral therapy (ART) and maintains an undetectable viral load has zero risk of sexually transmitting HIV—often described as U=U, or undetectable equals untransmittable.
HIV is caused by infection with human immunodeficiency virus. Transmission requires exposure to blood, semen or pre-seminal fluid, vaginal or rectal fluids, or breast milk from a person with transmissible HIV. Activities associated with higher likelihood of exposure include:
- Having anal or vaginal sex without a condom or preventive medicine when the partner’s HIV status or viral suppression is unknown
- Sharing needles, syringes, or other equipment used to inject drugs
- Having another sexually transmitted infection, which may increase susceptibility to HIV
- Using alcohol or drugs in ways that make it harder to use prevention strategies consistently
- Being exposed to HIV during pregnancy, childbirth, or breastfeeding when effective prevention and treatment are not in place
Having HIV is not determined by a person’s identity, and having multiple partners alone does not transmit HIV; risk depends on the type of exposure and the prevention measures used.
Effective prevention options include condoms, not sharing injection equipment, and pre-exposure prophylaxis (PrEP) for people who may be exposed to HIV. PrEP options include daily oral medicines and long-acting injections administered on a schedule determined by the specific medicine. Post-exposure prophylaxis (PEP) should be started as soon as possible and no later than 72 hours after a possible exposure. Regular testing helps people know their status. For people with HIV, taking ART and maintaining viral suppression—defined by CDC as a viral load below 200 copies/mL—prevents sexual transmission (U=U). HIV treatment during pregnancy and appropriate infant care can reduce transmission during pregnancy, labor, and delivery to 1% or less. With sustained viral suppression during and after pregnancy, transmission through breastfeeding is less than 1%, but not zero; infant-feeding decisions should be made with an experienced healthcare team.
Symptoms cannot confirm or rule out HIV; testing is the only way to know your HIV status. Some people have no symptoms after acquiring HIV. Others develop a flu-like illness, called acute HIV infection, usually within 2 to 4 weeks. Possible symptoms include:
- Fever or chills
- Rash
- Sore throat or mouth ulcers
- Swollen lymph nodes
- Fatigue, headache, or muscle aches
- Night sweats
After the acute stage, HIV may cause no symptoms for years even though the virus remains active. Without treatment, advanced HIV can cause persistent fever or night sweats, unexplained weight loss, long-lasting diarrhea, recurrent or severe infections, oral thrush, pneumonia, certain cancers, or neurologic problems. AIDS is diagnosed when HIV has severely damaged the immune system, such as when the CD4 count falls below 200 cells/mm³ or when certain opportunistic illnesses occur.
These symptoms can occur with many other conditions. If you may have been exposed to HIV, seek testing rather than waiting for symptoms. If the exposure occurred within the past 72 hours, seek urgent medical care to ask about PEP.
The only way to know whether you have HIV is to be tested. The main test types are:
- Antigen/antibody tests: A laboratory test using blood from a vein can usually detect HIV 18 to 45 days after exposure. A rapid antigen/antibody test using blood from a finger stick can usually detect HIV 18 to 90 days after exposure.
- Antibody tests: Most rapid tests and self-tests use blood or oral fluid and can usually detect HIV 23 to 90 days after exposure.
- Nucleic acid tests (NATs): These detect HIV RNA and can usually detect infection 10 to 33 days after exposure. They may be used when recent exposure or acute HIV is suspected, especially if an initial screening result is negative or indeterminate.
No HIV test detects infection immediately. The time between exposure and reliable detection is called the window period, and antiretroviral medicines used for PrEP or PEP may delay detection. A negative result after a recent exposure may therefore need repeat testing. A reactive laboratory antigen/antibody test is followed by an HIV-1/HIV-2 antibody differentiation test; if that result is negative or indeterminate, an HIV-1 NAT is used to evaluate for acute infection. A positive self-test or other rapid test must be confirmed in a healthcare setting.
After HIV is diagnosed, care typically includes a medical history and examination plus confirmation of HIV status if prior documentation is unavailable, a CD4 count, HIV viral load, drug-resistance testing, complete blood count, chemistry tests including kidney and liver function, urinalysis, and screening for hepatitis B and C, tuberculosis, sexually transmitted infections, and other conditions as appropriate. Pregnancy testing, vaccination review, and assessment for opportunistic infections may also be indicated. Additional tests—such as HLA-B*5701 before abacavir or cryptococcal antigen testing in people with advanced immune suppression—are selected according to the planned regimen, CD4 count, symptoms, and clinical circumstances.
Antiretroviral therapy (ART) is recommended for everyone with HIV and should be started at diagnosis or as soon as feasible. ART does not cure HIV, but it can reduce the viral load to an undetectable level, protect and restore immune function, prevent progression to AIDS, and support a long, healthy life.
Most initial treatment uses a combination regimen, often available as one pill taken once daily. Some people who are already virally suppressed may be eligible for long-acting injectable treatment. The best regimen depends on factors such as other health conditions, pregnancy potential, hepatitis B status, prior PrEP or PEP use, drug-resistance results, kidney and liver function, drug interactions, access, and patient preferences.
- Take ART as prescribed: Consistent treatment helps maintain viral suppression and prevents drug resistance.
- Monitor treatment: Viral load is the main measure of treatment response. CD4 counts and other laboratory tests are monitored based on immune status, treatment, and clinical needs.
- Prevent transmission: A person who takes ART and maintains viral suppression—a viral load below 200 copies/mL—has zero risk of sexually transmitting HIV (U=U). Condoms can still help prevent other sexually transmitted infections and pregnancy.
- Prevent and manage other illnesses: Care may include vaccines, screening and treatment for coinfections and chronic conditions, and medicines to prevent certain opportunistic infections when CD4 counts are low.
- Support overall health: Mental health care, substance-use support, nutrition, exercise, sleep, and help addressing barriers to medication or appointments can improve well-being and continuity of care.
Do not stop or change HIV medicines without speaking with an HIV healthcare professional. Treatment interruptions can allow the viral load to rebound and may increase the risk of illness, transmission, and drug resistance. Report side effects and review all prescription medicines, over-the-counter products, and supplements because interactions can occur.