This type of pneumonia is rare but can be dangerous for those with weakened immune systems. Treatment and diagnosis processes have come a long way in the last few decades.

Pneumocystis pneumonia (PCP) is an infection caused by a fungus called Pneumocystis jirovecii. PCP is a serious infection that most often develops in people with weakened immune systems. The infection is relatively rare in the general population.

The “C” in PCP comes from its previous name. There was a shift in understanding and knowledge about this infection in the 1980s when hospitals began seeing the number of people with it rise among those with HIV and AIDS. Before the 1980s, P. jirovecii was called P. carinii and was classed a protozoal infection. The “C” in the acronym PCP originally stood for carinii.

Although this is no longer correct, the acronym has stayed the same to avoid confusion. Keep reading to learn more about this rare form of pneumonia.

The fungus that causes PCP can live in the lungs of most people without causing symptoms. The U.S. Centers for Disease Control and Prevention (CDC) reports that up to 20% of adults carry the fungus at any time. Most people’s bodies typically remove the fungus without issue after a few months.

But people with weakened immune systems can develop serious infections when they contract the fungus that causes PCP. This is most commonly seen in people who have HIV or AIDS. About 30% to 40% of people with PCP have HIV or AIDS.

Other people who are at risk of PCP include people:

How common is Pneumocystis pneumonia?

There are no tracked statistics for PCP in the United States. Data from 2017 estimated that about 10,590 Americans were hospitalized with PCP during that calendar year. But there aren’t overall statistics and data.

It’s known that before the AIDS epidemic in the 1980s, PCP was extremely rare. During the height of the AIDS epidemic and before the development of today’s AIDS medications, around 75% of people with AIDS developed PCP.

These numbers have dropped in modern times, but PCP is still a concern for people with AIDS and other conditions that weaken their immune systems. PCP is also a concern in many countries around the world with developing healthcare systems.

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Symptoms of PCP are similar to symptoms of other types of pneumonia. They can include:

It’s a good idea to contact a healthcare professional if you’re experiencing any of these symptoms, especially if you’ve had them for more than a few days.

How to prevent Pneumocystis pneumonia

Some people who are at high risk of PCP, such as people with HIV or AIDS or people who’ve received organ or stem cell transplants, might be prescribed medication to help prevent PCP.

Typically, this involves a medication called co-trimoxazole (TMX/SMX). You and a healthcare professional can discuss if preventive medication is right for you. There’s no vaccine to prevent PCP.

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You’ll likely have a round of tests to confirm a diagnosis of PCP. This commonly includes:

  • Blood tests: Blood tests such as complete blood counts (CBCs) can help find your levels of white blood cells and can indicate an infection. Another blood test looks for a part of fungal cells called D-glucan.
  • Blood gas tests: You might have your arterial blood gas and venous blood gas taken to test the levels of oxygen and carbon dioxide in your blood.
  • Sputum exam: A sputum exam tests mucus that you cough into a collection tube for PCP-causing fungus.
  • X-ray: An X-ray can take images of your chest and check for buildup in your lungs.
  • Bronchoscopy: A bronchoscopy is a test that uses a small and narrow tube called an endoscope that’s inserted into your airways to get a better look at inflammation and damage. It can provide sputum samples as well as biopsies.
  • Lung biopsy: During a lung biopsy, a piece of your lung tissue will be removed so that it can be tested in a lab.

PCP is a serious infection. People with PCP need medical treatment to resolve the infection. If PCP isn’t treated, it can be fatal.

Treatment for PCP most often involves co-trimoxazole medication given as oral medication or through an intravenous (IV) line. Typically, 3 weeks of treatment are required. Your healthcare team will be monitoring your progress closely, so be sure to ask them if you have any questions about your treatment for PCP.

You might also receive treatment to relieve your symptoms, such as medication to bring down fever, rehydration liquids, and pain-relieving medications.

Get involved

While we do have treatments for PCP, researchers are still looking to improve the process. If you’d like to get involved in the search for new and better treatments, check out to see what studies are currently looking for participants.

Make sure to discuss any trials with a doctor or healthcare professional, especially if it will involve any changes to your current treatment regimen.

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The exact cost for PCP treatment will depend on your insurance plan and on factors such as the brand of co-trimoxazole you receive, if you need additional treatments for symptoms, and if you need hospitalization.

Your deductible, copayments, and the other details of your insurance plan will also make a difference in your final price.

PCP has an umbrella International Classification of Diseases, 10th revision (ICD-10) diagnostic billing code of B59. All treatments will fall under this code when they’re billed to your insurance. You can use this code to search your insurance coverage information to see what’s listed.

Your plan might specify that only certain medications and treatments are covered for PCP. Make sure to check with them for the most up-to-date information.

PCP can be fatal. Without treatment, PCP can lead to respiratory failure and to complications, such as a collapsed lung or fluid in your chest (pleural effusion).

Early treatment can help prevent these complications. Today, fewer people develop PCP than in the past thanks to better understanding and testing methods.

The introduction of medications for HIV and AIDS, especially antiretroviral therapy, has greatly reduced the number of people with PCP in the United States. But because the infection is so severe, the CDC still classifies PCP as a substantial public health concern.

PCP is a rare and serious fungal infection that primarily affects people with weakened immune systems.

This infection is most common in people with HIV and AIDS, but it can also occur in people who’ve had organ transplants and stem cell transplants and other people whose immune systems have been weakened due to conditions or medications.

Symptoms of PCP include fever, difficulty breathing, and fatigue. Medical treatment of PCP is important. Without treatment, PCP can be fatal. Treatment typically involves 3 weeks of co-trimoxazole medication orally or by an IV line.