What Is Pneumocystis Pneumonia?

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Pneumocystis pneumonia—often referred to by the acronym PCP—is a potentially life-threatening condition in which fluid builds up in the lungs and causes inflammation.

PCP is caused by a tiny fungus called Pneumocystis jirovecii that is common in the environment. Pneumocystis pneumonia has a long recorded history, going as far back as 1909. In the 1940s and 1950s, pneumocystis pneumonia was the cause of the pneumonia epidemics affecting premature and malnourished infants.

In the 1980s, PCP became the leading cause of death in people with AIDS. To this day, the majority of PCP cases are seen in people with human immunodeficiency virus (HIV), but this fungus affects those with other underlying medical conditions as well. 

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Most humans are exposed to the Pneumocystis jirovecii fungus in childhood. In healthy children, it often develops along with common cold symptoms and doesn’t turn into anything severe.

Pneumocystis jirovecii spreads through the air. While most people have a robust immune system that is capable of defending against this fungus, those with weakened immune systems may be unable to fight off this infection. 

This article discusses the risk factors, symptoms, diagnosis, treatment, and prevention of PCP.

Risk Factors

PCP can be a life-threatening condition for people with weakened immune systems. Certain conditions and medications can increase your risk for PCP, including but not limited to:

  • Previous Pneumocystis jirovecii infection
  • HIV
  • Cancer—especially cancers that affect the blood, like leukemia
  • Organ transplant
  • Stem cell transplant
  • Rheumatic diseases
  • Immunosuppressive medications
  • Severe malnutrition

Those who have a low CD4 cell count in their blood are at the highest risk for pneumocystis pneumonia. While CD4 levels are often tested for in people with HIV, they're also checked in people with the above conditions. 

Oral Thrush

Oral thrush is a fungal infection that mainly affects the mouth and throat. One study shows that those who experience oral thrush have almost a 30% chance of developing a PCP infection within 6 months.


Symptoms of pneumocystis pneumonia may vary between those in people with HIV and those in people who have cancer or are on immunosuppressive medications. Symptoms of pneumocystis pneumonia come on gradually in many people, and it can take weeks to notice an onset of symptoms.  

Most Common Symptoms

  • Fever
  • Feeling like you can’t take a deep breath
  • Dry cough
  • Sudden, sharp chest pain
  • Malaise (a general feeling of not being well)
  • Fatigue
  • Diarrhea
  • Weight loss


PCP is not always the most obvious illness to diagnose. It can start by mimicking the same symptoms as a cold or flu, which is why additional tests are required to diagnose PCP.

Physical Exam

Your healthcare provider will start by discussing your symptoms. The doctor will use a stethoscope to listen for anything unusual in your lungs. 


After your medical exam, you will likely need a chest X-ray to see if there’s an infection in your lungs. However, an X-ray is not always conclusive when it comes to PCP. In fact, a chest X-ray can appear normal in up to 25% of patients diagnosed with PCP.

CT Scan

If your healthcare provider suspects a PCP infection but you have an X-ray that seems normal, they may request a computed tomography scan (CT scan). A CT scan is able to provide a better image of the lungs than an X-ray.

Because a CT scan will expose you to more radiation than an X-ray and also costs more, your provider will start with an X-ray first.

Induced Sputum Test

The surest way to diagnose PCP is through a sputum culture.

During this test, you will breathe in a saltwater mist that will cause you to cough up mucus from the lungs. After a sample is collected, it will be sent to a lab. In the lab, the sample will be observed under a microscope to look for the fungus. 

A bronchoalveolar lavage is another way to collect sputum. It uses a bronchoscope to collect a sample from the lungs and, according to several sources, is common and useful in diagnosing fungal infections, especially to differentiate between Pneumocystis jirovecii and other fungi.

Pulmonary Function Test (PFT)

After being diagnosed with PCP, you will have a pulmonary function test to see how well the lungs are working.

A PFT looks at how much air you breathe in and out, how fast you breathe out, and the amount of oxygen moving from your lungs into your blood.


There are multiple options for treating PCP. The treatment you receive will depend on many factors, including the severity of your symptoms and if hospitalization is needed.

If you have a mild case of PCP, you'll be able to treat yourself at home by taking prescription medication such as Bactrim. If your case falls in the moderate category, you will be given a prescription steroid to help reduce the inflammation and damage in your lungs.

While some people are successful at treating PCP at home, many others need to be treated in the hospital. While in the hospital, you will receive hydration and medication through an intravenous (IV) drip. You will likely receive supplemental oxygen; in severe cases, you will be put on a ventilator.

Most treatment plans for PCP will last about three weeks. Many people will begin feeling better within about four to seven days after starting treatment. However, how quickly you feel better will depend on:

  • How strong your immune system is
  • How severe your infection is
  • How quickly you start treatment

While recovering, it's crucial to stay hydrated, get plenty of rest, and avoid others who are sick. The last thing you want to do when fighting PCP is pick up another infection.

PCP and Cough Medicine

While it seems reasonable to take cough medicine, it's important to only take cough medicine at night, when trying to get a full night's rest. The cough is an important mechanism your body uses to get rid of a lung infection. If you don't cough at all, your lungs can't get rid of the mucus, and the infection only worsens.


PCP can be more complicated to prevent than other forms of pneumonia. Prevention relies on following all recommendations of your healthcare provider. If you have HIV, it’s essential to take anti-HIV meds to keep your CD4 count above 200.

Eating Healthy

Nutrition is essential to keep your immune system strong. Eating healthy includes getting protein with every meal, along with foods containing vitamins and minerals. Protein helps your body repair damaged cells and keeps existing cells healthy.

Avoid Alcohol

Many drugs interact poorly with medications. In some cases, alcohol will interfere with the medicine you're taking. When you’re sick, avoiding alcohol is crucial in order to give your body and the medication the chance to work to their full ability. 

Mental Health

Keeping your mental health in check is essential. Chronic or excessive stress, anxiety, and depression will weaken your immune system. Even the slightest improvement in your stress levels can significantly benefit your body's ability to fight off any infection, including pneumonia.

2 Sources
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  2. Kanne JP, Yandow DR, Meyer CA. Pneumocystis jiroveci pneumonia: high-resolution CT findings in patients with and without HIV infectionAmerican Journal of Roentgenology. 2012;198(6):W555-W561. doi:10.2214/AJR.11.7329