HIV/AIDS

What are HIV and AIDS?

HIV attacks and destroys cells of the body's immune system. This damage progressively weakens the body's ability to fight infections and certain cancers.

The most advanced stage of HIV infection is known as AIDS.

People with AIDS are at great risk of getting very sick from conditions that are more common and more severe in people with weakened immune systems. These conditions include viral infections that cause skin tumors and pneumonia; fungal infections of the mouth, lungs, and genitals; and certain cancers.

AIDS was first reported in the United States in 1981; it is now recognized that HIV is a major worldwide epidemic.

Today, most people with HIV do not develop AIDS thanks to highly effective treatments that stop progression of HIV and allow people with HIV to live long, healthy lives. For this reason, this information focuses mostly on HIV instead of AIDS.

HIV.gov has a more comprehensive description of HIV and AIDS.

People with HIV experience different symptoms in the early and late stages of infection.

Acute HIV Infection

A few weeks after getting HIV, many people have flu-like symptoms, which may last days or weeks. These symptoms can include fever, headache, tiredness, and enlarged lymph glands in the neck and groin area. Some people may have no symptoms.

However, even if people with HIV feel healthy, the virus is still affecting their bodies. Once HIV enters the body, it infects large numbers of CD4+ cells and rapidly spreads throughout the body and into many organ systems.

During this early period, HIV is present in large amounts in genital fluids and in blood and can be passed to others.  

Chronic HIV Infection

In the next stage of HIV infection, the virus still multiplies, but at very low levels. People may not feel sick or have any symptoms.

If they are not getting treatment for HIV during this stage, they can still pass the virus to other people. Getting and staying on treatment prevents passing HIV to others.

Without HIV treatment, people can stay in this stage for a decade or more, although some move through this stage faster.

With treatment, HIV is only present in very small amounts in genital fluids and blood, or it may not be detectable at all. People with low or undetectable levels of HIV may never develop AIDS.

AIDS

AIDS is the most advanced stage of HIV, when a person's immune system is severely weakened and has difficulty fighting infections and certain cancers. At this stage, serious symptoms develop, such as:

• Rapid weight loss
• Serious infections
• Pneumonia
• Recurrent fevers
• Prolonged swelling of the lymph glands
• Skin blotches
• Prolonged diarrhea
• Sores of the mouth, anus, or genitals
• Memory loss
• Depression
• Other neurologic disorders

In the United States, most people with HIV do not develop AIDS thanks to highly effective treatments that stop progression of the virus.

HIV.gov has more comprehensive information about the symptoms of HIV.

HIV passes between people through blood and certain other body fluids, including semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk.

For transmission to occur, HIV present in these fluids must get into the bloodstream through a mucous membrane (found in the rectum, vagina, penis, and mouth), open cuts or sores, or by direct injection.^1,2

The most common ways that HIV can be passed from person to person include:

• Having anal or vaginal sex with someone who has HIV without using condoms or medicines to prevent or treat HIV. Worldwide, most new HIV acquisitions occur through sex. Women are particularly at risk of acquiring HIV through heterosexual sex. Having another sexually transmitted disease (STD) may increase a person’s risk of getting or transmitting HIV. For more information, see the Centers for Disease Control and Prevention's STDs and HIV Fact Sheet.
• Sharing needles, syringes, or other injection drug equipment with someone who has HIV.
• Perinatal transmission, which refers to HIV transmission from mother to child during pregnancy, labor and delivery, or breastfeeding. Pregnant women with HIV can prevent perinatal transmission by taking anti-HIV drugs. Additionally, in areas of the world where infant formula and safe water are available, women with HIV are recommended to avoid breastfeeding their children. Read more about preventing perinatal transmission of HIV.

In very rare cases, HIV also can be transmitted through other means, including oral sex, biting, deep open-mouth kissing, and pre-chewed food. The only known cases of transmission through pre-chewed food are among infants and involved blood from a caregiver’s mouth mixing with the food before feeding it to the infant.³ HIV also can be acquired through donated blood products or organ or tissue transplants, but this is rare today because of testing of the blood supply and organ and tissue donations.

How is HIV not transmitted?

HIV cannot be transmitted by:

• Contact with saliva, tears, or sweat
• Shaking hands
• Hugging
• Sharing food utensils
• Swimming in the same pool
• Using the same toilet seats
• Bites from insects or other animals

There is no evidence that HIV is spread by:

• Contact with saliva, tears, or sweat
• Shaking hands
• Hugging
• Sharing food utensils
• Sharing linens, like towels and bedding
• Swimming in the same pool
• Normal contact children experience in schools and homes
• Using the same telephone
• Using the same toilet seats
• Bites from insects or other animals

Anyone can get HIV, regardless of sexual orientation, race, ethnicity, gender, age, or geographic location.

Certain groups of people are at higher risk for getting HIV because of certain factors, such as engaging in risk behaviors. For example:

• HIV is mainly spread by having anal or vaginal sex without a condom or without medications to prevent or treat HIV. Risk behaviors such as having condomless sex and having multiple sexual partners are common among teens and young adults, who have very high rates of HIV compared to other Americans.
• Babies born to mothers with HIV can get HIV before or during birth or through breastfeeding, although effective prevention strategies can nearly eliminate the risk of this form of transmission.
• People with other sexually transmitted infections, such as chlamydia, gonorrhea, syphilis, bacterial vaginosis, and herpes, increase their risk of getting HIV if they are exposed to the virus through sex or blood exposure.
• Using drugs can increase risk. Sharing needles, syringes, or other drug injection equipment can spread HIV. Drug and alcohol use also can impair judgement and lead to risk behaviors like having sex without a condom or having multiple sexual partners.

The Centers for Disease Control and Prevention has more information about factors that increase HIV risk.

Risk Factors Specific to Adolescents

Many factors can increase or decrease HIV risk among youth. The Centers for Disease Control and Prevention's (CDC) National Youth Risk Behavior Survey and other CDC data have identified the following leading risk factors that can increase adolescents' and young adults' risk of HIV:¹

• Use of alcohol or drugs before sex. This can affect decision making about whether to engage in sex or to use condoms during sex.
• Not using an HIV prevention method during sex. Using condoms or taking medicine to prevent or treat HIV are highly effective HIV prevention options.
• Sex with multiple partners. The more sexual partners a person has, the more likely they are to be exposed to HIV or other sexually transmitted infections.
• Male–male sex. Young men who have sex with men, especially those who are Black/African American and Hispanic/Latino, have high rates of new HIV diagnoses. Anal sex is the riskiest type of sex for getting or transmitting HIV.
• Sharing needles, syringes, or other drug injection equipment.

Additional factors that can increase a young person’s chance of getting or transmitting HIV include inadequate education about safe sex, having older sexual partners, and having another sexually transmitted disease. Youth also have low rates of use of pre-exposure prophylaxis (PrEP), a medication taken to prevent getting HIV.

The most common tests examine a blood sample for evidence that a person's body is fighting HIV. These tests detect HIV antibodies, which are substances the body creates in response to infection. Some tests look for both antibodies and an antigen, a substance the virus makes before antibodies develop.

However, no HIV test can detect HIV immediately after infection. This is because it takes some time for the immune system to produce enough antibodies for the antibody test to detect. The time between when a person gets HIV and when a test can accurately detect it is called the window period. The window period varies from person to person and also depends on the type of HIV test. Ask your healthcare provider about the window period for the test you had and whether you will need a follow-up test to confirm the results.¹

The Centers for Disease Control and Prevention (CDC) has more information about HIV testing.

Diagnosis in Children and Youth

There are special challenges in diagnosing HIV in infants and youth.

Because HIV antibodies pass from mothers with HIV to their infants, finding HIV antibodies in an infant does not indicate that the infant has HIV. Maternal HIV antibody in an HIV-negative infant can persist as long as 12 to 18 months before it disappears. Therefore, an HIV antibody test cannot be used to diagnose HIV in infants younger than age 18 months.

Scientists have developed highly accurate blood tests for diagnosing HIV in infants. One laboratory test, called polymerase chain reaction, can detect extremely small quantities of HIV's genetic material in an infant's blood and allow a diagnosis to be made in the first few months of life.

The challenge in youth is different: Many young people think they're not at risk for HIV. This makes them less likely to seek testing. As a result, CDC recommends routine HIV screening in healthcare settings starting at age 13 years. The U.S. Preventive Services Task Force recommends routine screening for HIV beginning at age 15 years or earlier for adolescents at increased risk.

HIV drugs keep the virus from multiplying in the body, which benefits the person with HIV and prevents transmission of the virus to others.

Research has firmly established that people with HIV who achieve and maintain an undetectable viral load—the amount of HIV in the blood—by taking HIV treatment as prescribed cannot transmit the virus during sex. An undetectable viral load also reduces the risk of HIV transmission during pregnancy, labor, and delivery to 1% or less, according to the Centers for Disease Control and Prevention. It also substantially decreases, but does not eliminate, the risk of HIV transmission through breastfeeding. 

People with HIV sometimes get other illnesses and complications related to HIV, even when the virus is well-controlled with treatment. These include co-infections like hepatitis C and tuberculosis, as well as non-infectious complications such as heart disease. People with advanced-stage HIV may develop serious opportunistic infections, like pneumocystis pneumonia or cryptococcal disease. There are treatments available for many of these other illnesses.

The National Institute of Allergy and Infectious Diseases has more information about HIV treatment research.

Today, numerous HIV prevention methods are available for use in combination or on their own. These range from pre-exposure prophylaxis (PrEP)—in which healthy people routinely take anti-HIV drugs to reduce their risk of getting HIV—to condom use. Scientists continue to develop new tools and techniques to prevent HIV, including work toward an HIV vaccine. The National Institute of Allergy and Infectious Diseases has more information about HIV prevention research.

Preventing Perinatal Transmission

Advances in HIV treatment and prevention have greatly decreased transmission of HIV from mother to child during pregnancy, childbirth, and breastfeeding. Prevention strategies and interventions can reduce this risk to 1% or less.¹

If you are pregnant or planning to become pregnant, experts recommend that you:

• Get an HIV test. If you know you have HIV, you can take steps to lower your risk of perinatal transmission.
• If you have HIV, take anti-HIV drugs for yourself and your child. You should take anti-HIV drugs during pregnancy, labor, and birth, and your child should take them for the first weeks of life.
• If you have HIV, avoid breastfeeding. HIV can pass to your child through breast milk. If you live in the United States or another country with safe water, formula feeding is best for prevention of HIV.

NICHD is heavily involved in developing ways to prevent perinatal transmission of HIV. Read about the research advances in this area through the links on the Publications and Resources page.