Pneumocystis pneumonia: a plague of the immunosuppressed

Pneumocystis carinii pneumonitis is a diffuse bilateral alveolopathy encountered in the immunocompromised host with cancer, a congenital immune deficiency disorder, an organ transplant, severe protein-energy malnutrition or recipients of immunosuppressive therapy for other conditions. The onset is abrupt with fever and tachypnea. No rales are heard and the roentgenogram reveals a diffuse alveolar disease. Once the pneumonitis is evident, the infection is usually fatal if no treatment is given. The diagnosis is best established by the demonstration of the causative organism in specimens obtained by open lung biopsy, or other invasive methods, and stained with Gomori's methenamine silver nitrate, toluidine blue O or polychrome stains. Of the two drugs available for treatment, trimethoprim-sulfamethoxazole is preferred over pentamidine isethionate because of relative difference in adverse effects. With either drug the recovery rate is about 75%. The infection can be prevented in high risk patients by the administration of trimethoprim-sulfamethoxazole prophylactically.