HIV infection

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HIV (human immunodeficiency virus) is a virus that attacks cells that help the body fight infection, making a person more vulnerable to other infections and diseases. It is spread by contact with certain bodily fluids of a person with HIV, most commonly during unprotected sex (sex without a condom or HIV medicine to prevent or treat HIV), or through sharing injection drug equipment.

If left untreated, HIV can lead to the disease AIDS (acquired immunodeficiency syndrome).

The human body can’t get rid of HIV and no effective HIV cure exists. So, once you have HIV, you have it for life.

Luckily, however, effective treatment with HIV medicine (called antiretroviral therapy or ART) is available. If taken as prescribed, HIV medicine can reduce the amount of HIV in the blood (also called the viral load) to a very low level. This is called viral suppression. If a person’s viral load is so low that a standard lab can’t detect it, this is called having an undetectable viral load. People with HIV who take HIV medicine as prescribed and get and keep an undetectable viral load can live long and healthy lives and will not transmit HIV to their HIV-negative partners through sex.

In addition, there are effective methods to prevent getting HIV through sex or drug use, including pre-exposure prophylaxis (PrEP), medicine people at risk for HIV take to prevent getting HIV from sex or injection drug use, and post-exposure prophylaxis (PEP), HIV medicine taken within 72 hours after a possible exposure to prevent the virus from taking hold. Learn about other ways to prevent getting or transmitting HIV.


For the most part, other infections — with bacteria, other viruses, fungi, or parasites — cause the more pronounced symptoms of HIV.



Muscle aches and joint pain.


Sore throat and painful mouth sores.

Swollen lymph glands, mainly on the neck.


Weight loss.


HIV can transmit when body fluids containing the virus come into contact with a permeable barrier in the body or small breaks in moist tissues of areas, such as the genitals.

Specifically, HIV can transmit via:



pre-seminal fluid

vaginal fluids

rectal fluids

breast milk

The virus cannot transmit through saliva, so a person cannot contract HIV through open-mouthed kissing, for example.

One of the main causes of HIV transmission in the U.S. is anal or vaginal intercourse. Transmission of HIV occurs when individuals do not use barrier protection, such as a condom, during intercourse or are not taking pre-exposure prophylaxis (PrEP), a treatment that aims to prevent HIV transmission among people with known risk factors.

Sharing equipment for injecting drugs is another main cause of HIV transmission in the U.S.

Less commonly, HIV transmits to babies during pregnancy, childbirth, or breastfeeding or chestfeeding.

There is also a chance of transmission through blood transfusions, though the risk is extremely low when blood donations undergo effective screening.

Risk factors

having unprotected anal or vaginal sex;

having another sexually transmitted infection (STI) such as syphilis, herpes, chlamydia, gonorrhoea and bacterial vaginosis;

sharing contaminated needles, syringes and other injecting equipment and drug solutions when injecting drugs;

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Stage 3 HIV reduces the body’s ability to combat a range of infections and associated complications and types of cancer.

Current treatment is often effective enough to keep many infections at bay. If a person with HIV does not receive treatment, latent infections that once caused minimal or no health problems can pose a serious risk. Doctors refer to these infections as opportunistic.

Below are some opportunistic infectionsTrusted Source that can signal to a doctor that a person has stage 3 HIV:

Candidiasis: A fungal infection that typically occurs in the skin and nails, but it often causes serious problems in the esophagus and lower respiratory tract in people with AIDS.

Coccidioidomycosis: Inhalation of the fungus Coccidioides immitis causes coccidioidomycosis. A doctor may refer to this infection in healthy people as valley fever.

Cryptococcosis: This is an infection with Cryptococcus neoformans fungus. It may involve any part of the body, but the fungus usually enters the lungs and triggers pneumonia. It may also lead to swelling of the brain.

Cryptosporidiosis: Infection with the protozoan parasite Cryptosporidium can lead to severe abdominal cramps and chronic, watery diarrhea.

Cytomegalovirus disease (CMV): CMV can cause a range of diseases, including pneumonia, gastroenteritis, and encephalitis, a brain infection. CMV retinitis is a particular concern for people with AIDS. This is an infection of the retina at the back of the eye, and it permanently impairs a person’s sight. It is a medical emergency.

Herpes: This results from infection with the herpes simplex virus (HSV). This virus usually transmits when people have anal or vaginal sex without using barrier contraception, such as a condom. It can also transmit through vaginal childbirth. A doctor may recommend that a person experiencing genital herpes close to delivery has cesarean delivery. This significantly lowers the risk of HSV transmitting to the baby.

Histoplasmosis: This fungal infection causes severe, pneumonia-like symptoms in people with advanced HIV. Histoplasmosis can also become progressive and widespread, affecting organs outside the respiratory system.

Tuberculosis (TB): The bacteria Mycobacterium causes TB. The bacteria can transfer through the air if a person with an active infection sneezes, coughs, or speaks. The signs and symptoms can include a severe lung infection, weight loss, a fever, and fatigue. It can spread to the brain and other organs.

Infections with mycobacteria: Types of mycobacteria, including Mycobacterium avium and Mycobacterium kansasii, are naturally present and tend to cause few problems. However, when a person has HIV, especially in the later stages, these infections can spread throughout the body and cause life threatening health issues.

Recurrent pneumonia: Many different pathogens can cause pneumonia, but Streptococcus pneumoniae bacteria can be one of the most dangerous for people with HIV. A vaccine for this bacterium is available, and everyone with HIV should receive it.

Pneumocystis jirovecii pneumonia: An infection with this fungus can cause breathlessness, a dry cough, and a high fever in people with suppressed immune systems, including some people with HIV.

Chronic intestinal isosporiasis: This occurs when the parasite Isospora belli enters the body through contaminated food and water, causing diarrhea, fever, vomiting, weight loss, headaches, and abdominal pain.

Recurrent Salmonella septicemia: When Salmonella bacteria enter the body, usually via contaminated food or water, they can circulate and overpower the immune system, causing nausea, diarrhea, and vomiting. In this case, a doctor may diagnose recurrent Salmonella septicemia.

Toxoplasmosis: Toxoplasma gondii is a parasite that inhabits warm-blooded animals, including cats and rodents, and is present in their feces. Humans contract the resulting infection, called toxoplasmosis, by inhaling contaminated dust or eating contaminated food. It can cause severe symptoms involving the lungs, retina, heart, liver, pancreas, brain, testes, and colon. To reduce the risk of contracting toxoplasmosis, wear gloves while changing cat litter and thoroughly wash the hands afterward.

Related health problems

A person with advanced HIV or an opportunistic infection may experience complications, including:

HIV-related encephalopathy: HIV can trigger encephalopathy, or inflammation in the brain. Doctors do not fully understand the underlying mechanisms.

Progressive multifocal leukoencephalopathy (PML): PML stems from infection with the John Cunningham virus. This virus is present in many people, and it usually lies dormant in the kidneys. If a person has a weakened immune system, possibly due to HIV or medications, such as those for multiple sclerosis, the John Cunningham virus attacks the brain, leading to PML. It can be life threatening and cause paralysis and cognitive difficulties.

Wasting syndrome: Wasting syndrome occurs when a person involuntarily loses 10%Trusted Source of their muscle mass through diarrhea, weakness, or a fever. Part of the weight loss may also involve fat loss.


The following strategies can prevent contact with HIV.

Using barrier protection and PrEP

Using condoms or other barrier protection, such as dental dams, when engaging in anal, vaginal, or oral sex can drastically reduce a person’s chances of contracting HIV and other STIs.

Transgender women and non-binary people assigned male at birth who have undergone vaginoplasty are at risk for HIV transmission when engaging in insertive vaginal sex with a partner who has a penis.

In their 2019 guidelines, the Preventive Services Task Force advises that doctors only approve PrEP for people with recent negative HIV tests.

They also approve a PrEP formation: a combination of tenofovir disoproxil fumarate and emtricitabine. They advise people who take PrEP to do so once a day.

The Food and Drug Administration (FDA)Trusted Source has also approved a second combination drug — tenofovir alafenamide and emtricitabine — as PrEP.

Learn more about PrEP for transgender people here.

Using safe injection practices

Intravenous drug use is a key means of HIV transmission. Sharing needles and other drug equipment can expose a person to HIV and other viruses, such as hepatitis C.

Anyone who injects any drug should do so with a clean, unused needle.

Needle exchange and addiction recovery programs can help reduce the prevalence of HIV.

Learn more about needle exchange programs and HIV here.

Avoiding exposure to relevant body fluids

To limit the risk of exposure to HIV, reduce contact with blood, semen, vaginal secretions, and other body fluids that can carry the virus.

Frequently and thoroughly washing the skin immediately after coming into contact with body fluids can also reduce the risk of infection.

To prevent transmission, healthcare workers use gloves, masks, protective eyewear, face shields, and gowns when exposure to these fluids is likely, and they follow established procedures.

Learn more about contracting HIV here.


While certain antiretrovirals can harm the fetus during pregnancy, an effective, well-managed treatment plan can prevent transmission to the fetus.

Vaginal deliveries are possible if the person with HIV controls the condition well.