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Pneumocystosis

Author: Marie Hartley, Staff Writer, 2009.

What is pneumocystosis?

Pneumocystosis is disease caused by infection with pneumocystis organisms. Pneumocystosis is an opportunistic infection, primarily seen in individuals with impaired immunity.

Pneumocystosis is also known as PCP (Pneumocystis carinii pneumonia). The parasite Pneumocystis carinii, was once considered a protozoan, but has recently been reclassified as a fungus, although debate still exists over the correct taxonomic classification. Pneumocystis organisms are commonly found in the lungs of healthy humans and other mammals. Recent DNA analysis has shown the existence of multiple species of Pneumocystis. This has led to the renaming of the organism that causes human disease to Pneumocystis jirovecii.

P. jirovecii is a ubiquitous parasite that is present worldwide. Most children have antibodies to Pneumocystis by age 3 or 4, suggesting prior exposure to the organism. In healthy individuals, P. jirovecii rarely causes disease. Pneumocystosis usually occurs in immunodeficient patients with:

What are the clinical features of pneumocystosis?

P. jirovecii infection is usually limited to the lungs, but can occasionally spread to other organs, including the skin. It has been estimated that 66% to 85% of all HIV infected individuals will have one or more episodes of pneumocystosis in their lifetime. Approximately 1% to 2.5% of all P. jirovecii infections spread outside the lungs (extra pulmonary). Involvement of the skin by P. jirovecii is even more rare.

How is pneumocystosis diagnosed?

The diagnosis of pneumocystosis is usually based on microscopic identification of P. jirovecii from bronchopulmonary (lung) secretions. Bronchopulmonary secretions can be obtained by: induced sputum (patient inhales a salt water mist to encourage a deep cough) bronchoalveolar lavage (a small tube is passed through the mouth or nose into the lungs, fluid is squirted into a small area of lung and is then recollected for examination) or lung biopsy.

Different techniques can aid microscopic identification of P. jirovecii:

Biopsy of any skin lesions, with subsequent staining and microscopy can also reveal the organism.

What is the treatment for pneumocystosis?

The drug of choice for treating P. jirovecii infection is trimethoprim-sulphamethoxazole (TMP-SMZ). Patients infected with HIV tend to respond to treatment more slowly than patients without HIV and require longer duration of therapy (3 weeks of treatment as opposed to 2).

Alternative treatments for pneumocystosis include pentamidine and atovaquone.

(TMP-SMZ) can also be used as a prophylactic (preventive) agent in patients with HIV and in other patients with impaired immunity. In patients who cannot tolerate TMP-SMX, other options include dapsone, dapsone plus pyrimethamine, atovaquone, and aerosolised pentamidine.

What is the prognosis in pneumocystosis?

Early diagnosis and treatment of pneumocystosis increases the likelihood of successful treatment. In patients with HIV infection, around 10-20% of cases will be fatal.

In patients without HIV infection, around 30-50% of cases will be fatal; the higher mortality rate is likely to be due to delayed diagnosis in this group.

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