Pneumocystis Pneumonia

Overview

Pneumocystis pneumonia (PCP) is a lung infection caused by a fungus called Pneumocystis jirovecii. The fungus is common in the environment, and many people are exposed without becoming ill. In people with healthy immune systems it rarely causes disease, but in those with weakened immunity it can cause a serious, sometimes life-threatening pneumonia.

PCP became widely recognized during the HIV/AIDS epidemic and remains an important infection in people with advanced HIV. It also affects others with suppressed immune systems, such as some cancer patients, organ transplant recipients, and people taking certain immune-suppressing medications. Prompt diagnosis and treatment are important because the infection can progress quickly.

Symptoms

Symptoms often develop gradually over days to weeks, especially in people with HIV, which can delay recognition. They may include:

• Shortness of breath, often worse with activity.
• Dry cough.
• Fever.
• Chest discomfort or tightness.
• Fatigue.
• Low oxygen levels, which can cause rapid breathing or a bluish tint to the lips in severe cases.

In people without HIV, such as transplant recipients or those on strong immune-suppressing drugs, symptoms may come on more suddenly and become severe more quickly. Worsening breathlessness is an important warning sign, and any new breathing symptom in a person with weakened immunity should be taken seriously and evaluated promptly, since the infection can advance rapidly.

Causes

PCP is caused by the fungus Pneumocystis jirovecii, which spreads through the air. Most exposure happens early in life without illness. The infection causes disease mainly when the immune system cannot keep the fungus in check. Situations that allow this include:

• Advanced HIV/AIDS with a low immune cell count.
• Cancers, especially blood cancers such as leukemia and lymphoma.
• Organ or stem cell transplantation.
• Long-term use of corticosteroids or other immune-suppressing medications.
• Certain inherited or acquired immune deficiencies.

Risk Factors

The main risk factor is a weakened immune system. Specific groups at higher risk include:

• People with HIV who have a low immune cell (CD4) count and are not on effective treatment or preventive medication.
• People receiving chemotherapy or other cancer treatment.
• Organ and bone marrow transplant recipients.
• People taking high-dose or long-term corticosteroids or other drugs that suppress immunity.
• Those with certain primary immune deficiencies.

Diagnosis

Diagnosis combines the clinical picture with imaging and tests to detect the fungus:

• Medical history and examination, paying attention to immune status and symptoms.
• Chest imaging, such as an X-ray or CT scan, which often shows a particular pattern in the lungs.
• Oxygen level measurement, which is often low.
• Laboratory testing of respiratory samples, such as fluid from the lungs obtained through a procedure (bronchoscopy) or an induced sputum sample, to identify the fungus.
• Blood tests that may support the diagnosis.

Treatment

PCP is treated with specific anti-infective medication. Key points include:

• The standard treatment is the antibiotic combination trimethoprim-sulfamethoxazole, given for about three weeks. Alternative medications are used for people who cannot take it.
• Corticosteroids are often added for moderate to severe cases with low oxygen levels to reduce inflammation in the lungs.
• Oxygen and supportive care, and in severe cases breathing support in the hospital.
• Managing the underlying condition, such as starting or improving HIV treatment, with timing guided by the care team.

With prompt treatment many people recover, but PCP can be serious and even life-threatening, especially when diagnosed late or when oxygen levels are very low, so early care is important. Treatment usually requires close monitoring, and people who are very ill may need care in the hospital. After recovery, ongoing preventive medication is often continued for as long as the immune system remains significantly weakened.

Prevention

For people at high risk, PCP can often be prevented:

• Preventive antibiotics, usually trimethoprim-sulfamethoxazole, are given to people with significant immune suppression, such as those with HIV and a low immune cell count or certain transplant and cancer patients.
• Effective HIV treatment to restore immune function lowers the risk.
• Following medical advice on immune-suppressing medications and monitoring.
• Seeking prompt care for new breathing symptoms if you have a weakened immune system.

When to See a Doctor

If you have a weakened immune system, contact your doctor promptly for new or worsening cough, fever, or shortness of breath, even if symptoms seem mild at first, because PCP can progress quickly.

Seek emergency care for severe shortness of breath, difficulty breathing at rest, chest pain, confusion, or a bluish color of the lips or face, which can indicate dangerously low oxygen levels and the need for immediate treatment.

Related Topics

Frequently Asked Questions

References

1. Centers for Disease Control and Prevention (CDC).
2. MedlinePlus, U.S. National Library of Medicine.
3. National Institutes of Health (NIH).
4. Mayo Clinic.