Medical Definition of Pneumocystis

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Pneumocystis: Pneumocystis jiroveci (previously classified as Pneumocystis carinii), the organism that causes pneumocystis pneumonia (PCP). Pneumocystis jiroveci is found worldwide, in humans and animals. Serologic evidence indicates that most healthy children have been exposed to it by age 3 to 4. Pneumocystis pneumonia (PCP) occurs in immunosuppressed individuals and in premature, malnourished infants.

The symptoms of pneumocystis pneumonia (PCP) include dyspnea (difficulty breathing), nonproductive cough, and fever. Chest X-rays show infiltrates in both lungs. Typically, in untreated PCP, increasing pulmonary involvement leads to death.

There is considerable debate over the classification of Pneumocystis. The diagnosis is confirmed by the identification of Pneumocystis jiroveci in induced sputum or bronchoalveolar lavage (BAL) material (washings of the respiratory tree). In situations where these two techniques cannot be used, transbronchial biopsy or open lung biopsy may prove necessary. In addition, immunofluorescence microscopy using monoclonal antibodies can identify the organisms with higher sensitivity than conventional microscopy.

Treatment is with medication.

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Last Editorial Review: 1/24/2017

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