An infection with various causes that can be dangerous if the immune system is weakened.

An opportunistic infection happens more often or is more serious in people with weakened immune systems than in people with healthy immune systems. Viruses, bacteria, fungi and parasites can cause these infections. They spread in various ways, such as by air, in body fluids, or in tainted food or water.

Opportunistic infection symptoms vary widely and can cause problems throughout the body. Symptoms could affect the skin, nails, genitals, or organs such as the lungs, liver, heart and brain. The exact symptoms that a person has depend on the type of infection and the health of the immune system.

Treatment for an opportunistic infection depends on the cause of the infection. For instance, antiviral medicine may be needed to treat an illness caused by a virus. Antibiotic medicines can help get rid of bacteria that cause an illness. Antifungal medicines can help treat an infection caused by fungus.