Skip to Main Content

Human Immunodeficiency Virus (HIV)

  • HIV is a retrovirus that impairs the immune system and causes AIDS
  • Symptoms include fever, chills, rash, night sweats, sore throat, muscle and joint pain, headache
  • Treatment includes antiretroviral therapy (ART) and medications to manage and prevent infections
  • Involves Infectious Diseases, AIDS Care Program
Related Terms:

Human Immunodeficiency Virus (HIV)


After four decades in the global human immunodeficiency virus (HIV) epidemic, the medical community has learned a great deal about HIV since the AIDS crisis that began in 1981, when the first case was identified. Given new treatments—and with proper care—many people diagnosed with HIV can live a normal life.  

HIV is a virus that’s most often spread through blood and bodily fluids, typically but not exclusively through sexual contact. It attacks and kills a certain type of white blood cell in the body, which weakens the immune system and makes it hard for people to fight off illnesses and infections. AIDS (acquired immune deficiency syndrome) is an advanced form of immune deficiency caused by HIV.  

About 1.2 million Americans are living with HIV, and nearly 38,000 people are diagnosed each year. HIV can affect people of all ages, races and genders, but certain groups are impacted more than others. HIV disproportionately affects Black and Latinx Americans. And more than two-thirds of people who are newly diagnosed in the U.S. are men who have sex with men (including gay and bisexual men).  

It’s estimated that roughly 13% of people with HIV don’t know that they have the disease. Treatments may help people with HIV maintain their health and quality of life for decades, but people with undiagnosed HIV don’t know that they should seek treatment. This is why it’s important for people to learn their HIV status so that if they have the condition, they can start treatment early, before experiencing complications.  

We have effective and simple combination antiretroviral treatment [ART] in a single tablet. Although we don’t have a cure for HIV, we can achieve a functional cure and prolong the years and quality of life of people living with HIV,” says Lydia Aoun-Barakat, MD, medical director of the Yale HIV Ambulatory Center. “The key is to get tested at least once for HIV, and if the person is at risk, they can be on pre-exposure prophylaxis [PrEP] therapy. If they are positive, they should seek a rapid start of ART.”

What is HIV?

HIV is a retrovirus that infects humans. The virus attaches itself to specific white blood cells, called CD4 T cells. These cells are important components of the immune system, helping to fight infections in the body. But HIV renders them harmful, triggering those cells to make multiple copies of itself while gradually destroying the T cells.  

A healthy person may have, on average, 750-1,500 CD4 T cells per microliter of blood. In someone with HIV, as that number starts to decline over time, the immune system has trouble warding off illness. Once people with HIV have fewer than 200 CD4 T cells per microliter of blood, they may experience serious illness or infection, and their diagnosis changes from HIV infection to AIDS.  

When HIV was first documented, in the early 1980s, there were no effective treatments for it, so the disease often progressed to AIDS, leading to the death of millions of people. Today, the disease has moved from fatal to treatable; medications may help people with HIV live for decades with a good quality of life.

How is HIV transmitted?

The virus is spread through bodily fluids, including blood, semen, vaginal fluids, and breast milk. It’s considered primarily a sexually transmitted disease, but this isn’t the only way that people may come into contact with these bodily fluids. People are commonly exposed to the virus by:

  • Having unprotected sex. Partners may spread HIV through vaginal or anal intercourse. Unprotected receptive anal sex carries the highest risk, because the delicate tissue within the anus may tear, providing the virus a direct path to the bloodstream. Tiny, imperceptible cuts or sores on the genitals, inside the mouth or around or within the anus may also increase the risk of HIV entering the bloodstream. Latex condoms and dental dams can lower the risk.
  • Sharing syringes or needles. People who inject drugs recreationally may contract HIV if they share needles or syringes with other people who are HIV-infected. Using sterile needles and syringes can lower this risk.
  • Being stuck by a needle in a health care setting. Doctors and nurses are occasionally stuck by used needles or syringes during the course of their work. Hospitals and doctor’s offices have created protocols to reduce the likelihood of this accidental exposure to HIV and by providing post-exposure prophylaxis.
  • Passing HIV to a baby. When a woman has HIV, she may pass the virus to her unborn child during pregnancy, labor, or delivery. Some babies who are born HIV-negative to an HIV-positive mother may get HIV through breast milk. Doctors can help women control their HIV to significantly reduce the risk of transmitting the virus to their children.
  • Receiving a blood transfusion. Decades ago, donated blood wasn’t screened as carefully as it is today, and many people who needed transfusions received HIV-positive blood, including many people with hemophilia, a bleeding disorder. Today, donated blood is screened very carefully within the U.S., and the risk of HIV transmission is estimated to be less than 1 in 2 million transfusions.

What are the symptoms of HIV?

People experience different symptoms at different stages of the disease. When people are first exposed to HIV, about half of them don’t initially notice any signs of illness. The other half have flu-like symptoms two to four weeks after they’re infected, then recover. Other symptoms may include:

  • Fever or chills
  • Swollen lymph nodes
  • Sore throat
  • Skin rash
  • Joint and/or muscle aches
  • Headaches
  • Nausea or vomiting
  • Diarrhea
  • Weight loss
  • Fatigue
  • Sores or ulcers in the mouth
  • Night sweats
  • Confusion
  • Meningitis

Once the initial symptoms disappear, people who don’t know their HIV status (or aren’t treated) may experience mild illness or may have no noticeable symptoms for about a decade. Even in those with no symptoms, levels of CD4 T cells drop over time.

What are the signs the illness has progressed from HIV to AIDS?

When someone’s T-cell count falls below 200 per microliter of blood, they may develop infections and illnesses including:

  • Oral thrush
  • Recurrent herpes
  • Chronic mouth ulcers
  • Chronic bacterial infections
  • Neurological problems
  • Kaposi’s sarcoma, a cancer that causes dark-colored lesions on the skin
  • Non-Hodgkin’s lymphoma or other forms of lymphoma
  • Cervical cancer
  • Recurrent pneumonia
  • Other lung infections
  • Cytomegalovirus
  • Tuberculosis
  • Toxoplasmosis
  • Parasitic infections
  • Wasting syndrome

How is HIV diagnosed?

A definitive HIV diagnosis is made with a blood test.  Health care providers will also take a medical history, asking about personal health history, sexual partners, and other lifestyle habits that may increase risk. Because initial symptoms may be vague or not present, a physical exam usually won’t help doctors diagnose HIV.  

The routine HIV test may not become positive for several weeks after infection. For this reason, people who suspect that they’ve been exposed to HIV may need to get re-tested after several weeks or have a specific test for the HIV viral load in the blood.  

Different blood tests look for:

  • HIV antibodies
  • HIV antibodies and antigens
  • HIV itself, during a nucleic acid test
  • HIV RNA, during a viral load test

  It’s also possible to test oral fluids, such as saliva, for HIV.

How often should someone get tested for HIV?

The Centers for Disease Control and Prevention (CDC) recommends:

  • One-time HIV testing for all people between the ages of 13 and 64
  • More frequent testing for people at increased risk
  • Testing among pregnant women, to minimize the risk of mothers transmitting HIV to their babies 

Routine HIV testing at health care visits can be helpful, since it is not uncommon for a person to be unaware that they have the virus. Starting treatment as early as possible improves the outlook.

How is HIV treated?

Doctors recommend treatment for all people with HIV, including those who are newly diagnosed, no matter what their CD4 T cell counts are. Treatment may reduce HIV to undetectable levels, improve CD4 T cell counts, and prevent HIV from progressing to AIDS. People must take medication daily and consistently to prevent HIV from becoming drug-resistant.  

Common HIV therapies include:  

  • Antiretroviral therapy, a combination of two or three drugs, which helps limit HIV from replicating, strengthens the immune system, and helps lower the risk of transmission
  • Antifungal medications, which may treat thrush and other fungal infections
  • Antibiotics, which may treat certain bacterial infections and pneumonia
  • Pneumococcal vaccine, which can lower the risk of pneumonia
  • Other vaccines, such as the flu shot and hepatitis B vaccine, which can lower the risk of illness
  • Pre-exposure prophylaxis (PrEP) therapy can lower the risk of HIV during sexual encounters or during drug usage among high-risk people
  • Post-exposure (PEP) therapy can lower the risk of HIV among people who are exposed to the virus, including health care workers, drug users, and sexual assault victims 

Antiretroviral therapy may also reduce the risk of HIV among certain people.  

What is the outlook for people with HIV?

There is no cure for HIV, but it can be managed as a chronic condition. People who are living with HIV who take their medication daily and see their doctors regularly may enjoy a fairly normal life.  

People who don’t seek treatment for HIV or AIDS may only live for about 3 years after the onset of AIDS.

What makes Yale unique in its treatment of HIV?

Yale established the first HIV clinic in the state of Connecticut and continues to care for the largest cohort of people living with HIV. 

“We provide a comprehensive and interdisciplinary team approach to HIV and offer state-of-the-art treatment with access to new drugs and clinical trials, in addition to cutting edge research,” says Dr. Barakat. “Furthermore, Yale was the first clinic in the state to offer PrEP to persons at risk for HIV. Through our talented and experienced providers and researchers, along with community partnership, Yale aspires to be in the forefront to ending the HIV epidemic.”