What Are Opportunistic Infections?
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 OIs 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. (Read more about CD4 count tests on HIV.gov’s Lab Tests and Results page.)
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
How Can You Prevent Getting Opportunistic Infections?
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?
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.
For detailed information about specific OIs, see the HHS Prevention and Treatment Guidelines for Adults and Adolescents with HIV.