Microbiology
Summary
The opportunistic fungus, Pneumocystis jiroveci, is known to cause pneumocystis pneumonia or PCP. This fungus primarily affects immunocompromised individuals, notably those with AIDS, with a significant correlation observed when the CD4 count drops below 200. As such, PCP is considered an AIDS-defining illness.
While P. jiroveci can infect healthy individuals, it often remains asymptomatic in them. However, those with compromised immune systems may present with symptoms like cough, fever, and dyspnea. On chest x-ray, a distinct ground-glass appearance may be observed, indicative of diffuse interstitial pneumonia. The definitive diagnosis is achieved through bronchoalveolar lavage or BAL, with subsequent methenamine silver staining of the sample showing disc-shaped yeast cells. In terms of management, Bactrim (trimethoprim-sulfamethoxazole) is recommended for treatment and prophylaxis, especially when CD4 counts fall below 200. For those allergic to sulfa, pentamidine serves as an alternative.
Lesson Outline
Don't stop here!
Get access to 128 more Microbiology lessons & 13 more medical school learning courses with one subscription!
FAQs
Pneumocystis pneumonia, also known as PCP, is a type of pneumonia caused by an organism called Pneumocystis jirovecii. This type of pneumonia is commonly seen in people with weakened immune systems, especially those with HIV/AIDS.
Pneumocystis jirovecii is thought to be spread through the air, being inhaled into the lungs. This means the organism is transmitted from person to person through respiratory droplets. Once inside the lungs of a susceptible individual, the organism can cause a potentially life-threatening infection like pneumocystis pneumonia.
AIDS-defining illnesses are diagnoses that signal the transition from HIV infection to AIDS. Pneumocystis pneumonia is listed as one of these illnesses because of its high incidence in people with severely compromised immune systems, specifically those with a CD4 count below 200 cells/µL.
In pneumocystis pneumonia, chest X-rays or CT scans often present a "ground-glass appearance," indicative of diffuse interstitial pneumonia. In laboratory evaluations, a bronchoalveolar lavage or lung biopsy might be performed to collect samples. The organism can be seen using a methenamine silver stain which stains the cyst walls of Pneumocystis jirovecii silver for better visualisation.
The first-line treatment for pneumocystis pneumonia is a combination of trimethoprim and sulfamethoxazole, commonly known as Bactrim. It is an antibiotic treatment that works to stop the growth of the Pneumocystis jirovecii organism. Pentamidine is often used as a second-line treatment for PCP in patients who cannot tolerate sulfa drugs.
