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Opportunistic Infections

Image of HIV virus Opportunistic infections (OIs) are infections that occur more frequently and are more severe in individuals with weakened immune systems, including people with HIV. OIs are less common now than they were in the early days of HIV and AIDS because better treatments reduce the amount of HIV in a person’s body and keep a person’s immune system stronger. However, many people with HIV still develop OIs because they may not know of their HIV infection, they may not be on treatment, or their treatment may not be keeping their HIV levels low enough for their immune system to fight off infections.

For those reasons, it is important for individuals with HIV to be familiar with the most common OIs so that they can work with their healthcare provider to prevent them or to obtain treatment for them as early as possible.

Most Common Opportunistic Infections

When a person living with HIV gets certain infections (called opportunistic infections, or OIs), he or she will get a diagnosis of AIDS, the most serious stage of HIV infection. AIDS is also diagnosed if a type of blood cell that fights infection (known as CD4 cells) falls below a certain level in persons with HIV. These blood cells are a critical part of a person’s immune system.

CDC has developed a list of OIs that indicate a person has AIDS. It does not matter how many CD4 cells a person has, receiving a diagnosis with any of these OIs means HIV infection has progressed to AIDS. HIV treatment can help restore the person’s immune system.

Following is a list of the most common OIs for individuals living in the United States. For more details, including signs and symptoms of specific OIs, please refer to the Opportunistic Infection pages at Additionally, CDC, the National Institutes of Health, the HIV Medicine Association of the Infectious Disease Society of America (HIVMA/IDSA), and other experts in infectious disease have published Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. While the guidelines are intended for healthcare professionals, some consumers may find them useful.

Candidiasis of bronchi, trachea, esophagus, or lungs This illness is caused by infection with a common (and usually harmless) type of fungus called Candida. Candidiasis, or infection with Candida, can affect the skin, nails, and mucous membranes throughout the body. Persons with HIV infection often have trouble with Candida, especially in the mouth and vagina. However, candidiasis is only considered an OI when it infects the esophagus (swallowing tube) or lower respiratory tract, such as the trachea and bronchi (breathing tube), or deeper lung tissue.
Invasive cervical cancer This is a cancer that starts within the cervix, which is the lower part of the uterus at the top of the vagina, and then spreads (becomes invasive) to other parts of the body. This cancer can be prevented by having your care provider perform regular examinations of the cervix
Coccidioidomycosis This illness is caused by the fungus Coccidioides immitis. It most commonly acquired by inhaling fungal spores, which can lead to a pneumonia that is sometimes called desert fever, San Joaquin Valley fever, or valley fever. The disease is especially common in hot, dry regions of the southwestern United States, Central America, and South America.
Cryptococcosis This illness is caused by infection with the fungus Cryptococcus neoformans. The fungus typically enters the body through the lungs and can cause pneumonia. It can also spread to the brain, causing swelling of the brain. It can infect any part of the body, but (after the brain and lungs) infections of skin, bones, or urinary tract are most common.
Cryptosporidiosis, chronic intestinal (greater than one month's duration) This diarrheal disease is caused by the protozoan parasite Cryptosporidium. Symptoms include abdominal cramps and severe, chronic, watery diarrhea.
Cytomegalovirus diseases (particularly retinitis) (CMV) This virus can infect multiple parts of the body and cause pneumonia, gastroenteritis (especially abdominal pain caused by infection of the colon), encephalitis (infection) of the brain, and sight-threatening retinitis (infection of the retina at the back of eye). People with CMV retinitis have difficulty with vision that worsens ever time. CMV retinitis is a medical emergency because it can cause blindness if not treated promptly.
Encephalopathy, HIV-related This brain disorder is a result of HIV infection. It can occur as part of acute HIV infection or can result from chronic HIV infection. Its exact cause is unknown but it is thought to be related to infection of the brain with HIV and the resulting inflammation.
Herpes simplex (HSV): chronic ulcer(s) (greater than one month's duration); or bronchitis, pneumonitis, or esophagitis Herpes simplex virus (HSV) is a very common virus that for most people never causes any major problems. HSV is usually acquired sexually or from an infected mother during birth. In most people with healthy immune systems, HSV is usually latent (inactive). However, stress, trauma, other infections, or suppression of the immune system, (such as by HIV), can reactivate the latent virus and symptoms can return. HSV can cause painful cold sores (sometime called fever blisters) in or around the mouth, or painful ulcers on or around the genitals or anus. In people with severely damaged immune systems, HSV can also cause infection of the bronchus (breathing tube), pneumonia (infection of the lungs) and esophagitis (infection of the esophagus, or swallowing tube).
Histoplasmosis This illness is caused by the fungus Histoplasma capsulatum. Histoplasma most often infects the lungs and produces symptoms that are similar to those of influenza or pneumonia. People with severely damaged immune systems can get a very serious form of the disease called progressive disseminated histoplasmosis. This form of histoplasmosis can last a long time and involves organs other than the lungs.
Isosporiasis, chronic intestinal (greater than one month's duration) This infection is caused by the parasite Isospora belli, which can enter the body through contaminated food or water. Symptoms include diarrhea, fever, headache, abdominal pain, vomiting, and weight loss.
Kaposi's sarcoma (KS) This cancer, also known as KS, is caused by a virus called Kaposi's sarcoma herpesvirus (KSHV) or human herpesvirus 8 (HHV-8). KS causes small blood vessels, called capillaries, to grow abnormally. Because capillaries are located throughout the body, KS can occur anywhere. KS appears as firm pink or purple spots on the skin that can be raised or flat. KS can be life-threatening when it affects organs inside the body, such the lung, lymph nodes or intestines.
Lymphoma, multiple forms Lymphoma refers to cancer of the lymph nodes and other lymphoid tissues in the body. There are many different kinds of lymphomas. Some types, such as non-Hodgkin lymphoma and Hodgkin lymphoma, are associated with HIV infection.
Tuberculosis (TB) Tuberculosis (TB) infection is caused by the bacteria Mycobacterium tuberculosis. TB can be spread through the air when a person with active TB coughs, sneezes, or speaks. Breathing in the bacteria can lead to infection in the lungs. Symptoms of TB in the lungs include cough, tiredness, weight loss, fever, and night sweats. Although the disease usually occurs in the lungs, it may also affect other parts of the body, most often the larynx, lymph nodes, brain, kidneys, or bones.
Mycobacterium avium complex (MAC) or Mycobacterium kansasii, disseminated or extrapulmonary. Other Mycobacterium, disseminated or extrapulmonary. MAC is caused by infection with different types of mycobacterium: Mycobacterium avium, Mycobacterium intracellulare, or Mycobacterium kansasii. These mycobacteria live in our environment, including in soil and dust particles. They rarely cause problems for persons with healthy immune systems. In people with severely damaged immune systems, infections with these bacteria spread throughout the body and can be life-threatening.
Pneumocystis carinii pneumonia (PCP) This lung infection, also called PCP, is caused by a fungus, which used to be called Pneumocystis carinii, but now is named Pneumocystis jirovecii. PCP occurs in people with weakened immune systems, including people with HIV. The first signs of infection are difficulty breathing, high fever, and dry cough.
Pneumonia, recurrent Pneumonia is an infection in one or both of the lungs. Many germs, including bacteria, viruses, and fungi can cause pneumonia, with symptoms such as a cough (with mucous), fever, chills, and trouble breathing. In people with immune systems severely damaged by HIV, one of the most common and life-threatening causes of pneumonia is infection with the bacteria Streptococcus pneumoniae, also called Pneumococcus. There are now effective vaccines that can prevent infection with Streptococcus pneumoniae and all persons with HIV infection should be vaccinated.
Progressive multifocal leukoencephalopathy This rare brain and spinal cord disease is caused by the JC virus. It is seen almost exclusively in persons whose immune systems have been severely damaged by HIV. Symptoms may include loss of muscle control, paralysis, blindness, speech problems, and an altered mental state. This disease often progresses rapidly and may be fatal.
Salmonella septicemia, recurrent Salmonella are a kind of bacteria that typically enter the body through ingestion of contaminated food or water. Infection with salmonella (called salmonellosis) can affect anyone and usually causes a self-limited illness with nausea, vomiting, and diarrhea. Salmonella septicemia is a severe form of infection in which the bacteria circulate through the whole body and exceeds the immune system’s ability to control it.
Toxoplasmosis of brain This infection, often called toxo, is caused by the parasite Toxoplasma gondii. The parasite is carried by warm-blooded animals including cats, rodents, and birds and is excreted by these animals in their feces. Humans can become infected with it by inhaling dust or eating food contaminated with the parasite. Toxoplasma can also occur in commercial meats, especially red meats and pork, but rarely poultry. Infection with toxo can occur in the lungs, retina of the eye, heart, pancreas, liver, colon, testes, and brain. Although cats can transmit toxoplasmosis, litter boxes can be changed safely by wearing gloves and washing hands thoroughly with soap and water afterwards. All raw red meats that have not been frozen for at least 24 hours should be cooked through to an internal temperature of at least 150oF.
Wasting syndrome due to HIV Wasting is defined as the involuntary loss of more than 10% of one’s body weight while having experienced diarrhea or weakness and fever for more than 30 days. Wasting refers to the loss of muscle mass, although part of the weight loss may also be due to loss of fat.

Preventing Opportunistic Infections

The best ways to prevent getting an OI are to get into and stay on medical care and to take HIV medications as prescribed. Sometimes, your health care provider will also prescribe medications specifically to prevent certain OIs. By staying on HIV medications, you can keep the amount of HIV in your body as low as possible and keep your immune system healthy. It is especially important that you get regular check-ups and take all of your medications as prescribed by your care giver. Taking HIV medications is a life-long commitment.

In addition to taking HIV medications to keep your immune system strong, there are other steps you can take to prevent getting an OI.

  • Use condoms consistently and correctly to prevent exposure to sexually transmitted infections.
  • Don’t share drug injection equipment. Blood with hepatitis C in it can remain in syringes and needles after use and the infection can be transmitted to the next user.
  • Get vaccinated – your doctor can tell you what vaccines you need. If he or she doesn’t, you should ask.
  • Understand what germs you are exposed to (such as tuberculosis or germs found in the stools, saliva, or on the skin of animals) and limit your exposure to them.
  • Don’t consume certain foods, including undercooked eggs, unpasteurized (raw) milk and cheeses, unpasteurized fruit juices, or raw seed sprouts.
  • Don’t drink untreated water such as water directly from lakes or rivers. Tap water in foreign countries is also often not safe. Use bottled water or water filters.
  • Ask your doctor to review with you the other things you do at work, at home, and on vacation to make sure you aren't exposed to an OI. For more information on international travel, please see Living with HIV: Travel Abroad.

CDC, the National Institutes of Health, the HIV Medicine Association of the Infectious Disease Society of America (HIVMA/IDSA), and other experts in infectious disease have published Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. While the guidelines are intended for healthcare professionals, some consumers may find them useful.

Treating Opportunistic Infections

If you do develop an OI, there are treatments available, such as antibiotics or antifungal drugs. Having an OI may be a very serious medical situation and its treatment can be challenging. The development of an OI likely means that your immune system is weakened and that your HIV is not under control. That is why it is so important to be on medication, take it as prescribed, see your care provider regularly, and undergo the routine monitoring he or she recommends to ensure your viral load is reduced and your immune system is healthy.

For healthcare professionals: You can learn more about treating OIs by referring to Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. The guidelines were developed by CDC, the National Institutes of Health, the HIV Medicine Association of the Infectious Disease Society of America (HIVMA/IDSA), and other experts in infectious disease.

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