Genius knowledge on Opportunistic Infections 2022

a man and a woman looking at the test tubes

Opportunistic infections (OIs) are infections that occur more frequently and are more severe in people with weakened immune systems, including people with HIV.

Many OIs are considered AIDS-defining conditions. That means if a person with HIV has one of these conditions, they are diagnosed with AIDS, the most serious stage of HIV infection.

What are Some of the Most Common Opportunistic Infections?

Some of the most common OIs in people living with HIV in the U.S. are:

  • Herpes simplex virus 1 (HSV-1) infection—a viral infection that can cause sores on the lips and mouth
  • Salmonella infection—a bacterial infection that affects the intestines
  • Candidiasis (thrush)—a fungal infection of the mouth, bronchi, trachea, lungs, esophagus, or vagina
  • Toxoplasmosis—a parasitic infection that can affect the brain

Visit CDC for a detailed list.

What Causes Opportunistic Infections?

OIs are caused by a variety of germs (viruses, bacteria, fungi, and parasites). These germs spread in different ways, such as in the air, in body fluids, or in contaminated food or water. They can cause health problems when a person’s immune system is weakened by HIV disease.

Who Is at Risk for Opportunistic Infections?

People with HIV are at greatest risk for OIs when the count of their infection-fighting CD4 cells falls below 200. However, some Opportunistic Infections can occur when a person’s CD4 count is below 500. That’s because weakened immune system makes it harder for the body to fight off HIV-related OIs.

Are Opportunistic Infections Common in People with HIV?

OIs are less common now than in the early days of HIV and AIDS when there was no treatment. Today’s HIV medicines (called antiretroviral therapy or ART) reduce the amount of HIV in a person’s body and keep the immune system stronger and better able to fight off infections.

However, some people with HIV still develop OIs for reasons such as:

  • they do not know they have HIV and so they are not on treatment
  • they know they have HIV but are not taking ART
  • they had HIV for a long time before they were diagnosed and so have a weakened immune system
  • they are taking ART, but their drug combination is not working as expected and is not keeping their HIV levels low enough for their immune system to fight off infections

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How Can You Prevent Getting Opportunistic Infections?

Prevent Opportunistic Infections infographic
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If you have HIV, the best thing you can do to stay healthy and prevent OIs is to take HIV medicine (called antiretroviral therapy or ART) exactly as prescribed and get and keep an undetectable viral load—a level of HIV in your blood so low that a standard lab test can’t detect it.

It is also important to stay in HIV medical care and get lab tests done. This will allow you and your health care provider to know when you might be at risk for OIs and discuss ways to prevent them.

Some of the ways people with HIV can reduce their risk of getting an OI include:

  • avoiding exposure to contaminated water and food
  • taking medicines to prevent certain OIs
  • getting vaccinated against some preventable infections
  • traveling safely

Can Opportunistic Infections Be Treated?

If you develop an OI, there are treatments available such as antiviral, antibiotic, and antifungal drugs. The type of medicine your health care provider prescribes will depend on the OI.

Once an OI is successfully treated, a person may continue to use the same medicine or an additional medicine to prevent the OI from coming back. Having an OI may be a very serious medical situation and its treatment can be challenging.

Most Common Opportunistic Infections in People Living with HIV

Since combination antiretroviral treatment for HIV became available, the number of people living with HIV who have had opportunistic infections has dropped drastically. If you start HIV treatment early and continue to take your HIV drugs as they are prescribed, you will keep your immune system strong and likely never get one of these OIs. This means you will also likely never be diagnosed with AIDS.

Some of the most common opportunistic infections in people living with HIV include:

KOpportunistic InfectionCauseLocationSymptomsWhen does it usually occur?Additional Information
CandidiasisFungus: overgrowth of yeast, most commonly Candida albicansMouth (oral thrush), throat, esophagus (food tube), vagina (birth canal)Whitish coating on tongue; painful swallowing or sense of food sticking in throat; itching, burning in genital areaMore likely to develop deeper in the body (e.g., esophagus) when CD4 < 200
Cytomegalovirus (CMV)VirusMost commonly eyes; also lungs, brain, and gutIn the eyes, CMV causes black spots (‘floaters’), blind spots, & distorted visionCD4 < 50Common infection in people both with and without HIV
Cryptococcosis (Crypto)FungusBrain and spinal cord; causes meningitis, which is an inflammation of the lining of the brain and spinal cord. It can also cause systemic blood infection or pneumonia.Headache, fever, general sense of feeling unwellCD4 < 50 
CryptosporidiosisParasiteGutLots of watery diarrhea, nausea, vomiting, stomach crampingCD4 < 100Since the parasite lives in contaminated water and stool, it is important to wash hands well after using the bathroom and to drink clean water
Mycobacterium avium complex (MAC)BacteriumMany different organsFever, chills, night sweats, weight loss, diarrhea, stomach painCD4 < 50Prophylaxis is no longer recommended but could be considered in those not taking ART
Mycobacterium tuberculosis (TB)BacteriumLungs; also liver, heart, gut, and brainCough, weight loss, fever, night sweats, tiredness. Symptoms usually worsen over several weeks, not days.Any CD4 count, but more likely to affect heart, gut, & brain with CD4 < 200CDC recommends pregnant women get tested for TB if not tested in year before pregnancy; also special considerations for treatment when pregnant
Pneumocystis pneumonia (PJP)FungusLungsShortness of breath, fever, dry coughCD4 < 200Prophylaxis recommended if CD4 < 200
Progressive multifocal leukoencephalopathy (PML)VirusBrainChanges to personality, thinking, vision, speech, or balanceCD4 < 200Treatment is HIV drugs
Toxoplasmosis (Toxo)ParasiteBrain, causing encephalitis (inflammation of the brain)Headache, fever, confusion, weakness, seizuresRare with CD4 < 200; usually in those with CD4 < 50Prophylaxis recommended if CD4 < 100; to avoid Toxo, do not eat uncooked meat or touch cat poop, i.e. avoid handling litter boxes

Opportunistic Infections and Women

Some opportunistic infections occur differently in women than in men:

  • Men are more likely than women to develop Kaposi sarcoma (KS)
  • Women are more likely than men to develop bacterial pneumonia and yeast infections

It is important for women living with HIV to have regular cervical cancer screenings and gynecological exams. Women can have abnormal cells grow on different parts of their reproductive systems (e.g., cervix, uterus, ovaries). This abnormal cell growth is called dysplasia and can lead to cancer. Dysplasia is often more severe and difficult to treat in women living with HIV than in HIV-negative women. Untreated dysplasia can lead to cervical cancer, which is a life-threatening illness and an AIDS-defining condition. For more information on women’s health exams, see our fact sheet Caring for a Woman’s Body.

In addition, it is important that women living with HIV have regular appointments with their HIV provider to check their overall health. If you see a health care provider regularly, he or she can help you prevent OIs, and diagnose and treat any infections early on. Ultimately, taking your HIV drugs regularly and staying as healthy as you can is the best way to avoid opportunistic infections. Properly taking your medications will keep your viral load undetectable and your CD4 count higher, thus making your immune system stronger and better able to fight off any type of infection.

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