Pneumocystis Pneumonia (PCP)

Medically Reviewed by Jonathan E. Kaplan, MD on February 12, 2024
4 min read

Pneumocystis pneumonia (PCP) is a serious infection that causes inflammation and fluid buildup in your lungs. It's brought on by a fungus called Pneumocystis jirovecii that spreads through the air.

This fungus is very common. Most people’s immune systems have fought it off by the time they're 3 or 4 years old. But it can make people who have weakened immune systems, like from HIV, very sick.

It's rare, but PCP can also affect other parts of your body, including your lymph nodes, liver, and bone marrow.

Early in the infection, you might not have symptoms, or they could be mild. They may include:

Symptoms usually come on slowly, over several weeks, in people who have HIV. In those whose immune systems are weak for another reason, they tend to start over a few days.

PCP usually happens in people who've had an organ transplant, who have HIV, who have blood cancers, or who take certain drugs for autoimmune diseases such as rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis.

In the late 1980s, before there was medicine to treat HIV, about three-quarters of people who had AIDS got PCP. Antiretroviral therapy (ART) now keeps people with HIV from getting AIDS, and not many of them get PCP. But in people who have AIDS, it’s still the most common opportunistic infection -- a disease that happens more often or is worse in people with weak immune systems.

You're most likely to get PCP when your CD4 cell count (a type of white blood cell) is less than 200. People who have HIV and get PCP are eight times more likely to need to stay in the hospital than those who get PCP but don’t have HIV. Even with treatment, PCP can be deadly for people who have AIDS.

Many other conditions can cause similar symptoms in people who have HIV, including:

A technician will use a microscope to look for traces of the fungus in fluid or tissue from your lungs. Your doctor will help you cough up fluid. Or they might use a special tool called a bronchoscope, which goes through your mouth and into your airways, to take a sample. They could also do a biopsy, using a needle or a knife to remove a tiny amount of cells from your lung.

A test called PCR (polymerase chain reaction) makes copies of specific pieces of DNA so it can find smaller amounts of the fungus in samples.

You might also get a chest X-ray or blood tests to check for low oxygen levels or high levels of something called beta-D-glucan.

Doctors usually treat PCP with two antibiotics, trimethoprim and sulfamethoxazole, also known as TMP/SMX (Bactrim, Cotrim, Septra). Depending how sick you are, you'll get them in pills to swallow or through a needle in your vein (by IV) at the hospital.

Other drugs that fight the infection include:

Corticosteroids can help when you have low oxygen levels.

No vaccine can keep you from getting this type of pneumonia. If you have HIV, the best way to prevent PCP is to keep up with your ART, which raises your CD4 count so your immune system is better able to fight off infections.

The medication that treats PCP can also prevent it. Your doctor may give it to you when:

  • You've had PCP before.
  • Your CD4 count is below 200.
  • You're taking drugs that suppress your immune system.

If you get PCP, your doctor may want you to keep taking the medicine after it goes away so you don't get it again.