Introduction 

-Pneumocystis pneumonia is caused by Pneumocystis jirovecii, previously known as Pneumocystis carinii 

-it was previously thought to be a protozoan, but now recognized as a fungus

-it is an extracellular pathogen 

-It has morphologically distinct forms: thin-walled trophozoites and thick-walled cysts 

-It is the most frequent serious complication of HIV infection in the United States

–it is the most common opportunistic infection among AIDS patients

-It is the most common identifiable cause of death in patients with AIDS

Symptoms & Signs 

-In the absence of immunosuppression, P. jiroveci does not cause disease

-It can cause disease in patients with immunocompromised conditions – AIDS, or organ transplantation, and chemotherapy 

– PCP is often the initial opportunistic infection that establishes the diagnosis of AIDS, often when the CD4+ T-lymphocyte count has fallen below 200 cells/mm3

-non-productive cough out of proportion to physical findings, fever, fatigue, weight loss, dyspnea, marked hypoxemia, and spontaneous pneumothorax

Diagnosis 

Diagnostic techniques: Routine sputum, induced sputum, transtracheal aspiration, Bronchoalveolar lavage, transbronchial biopsy, open lung biopsy, needle aspirate 

Histology: Alveoli filled with trophozoites, cysts, alveolar cells, monocytes, producing a distinctive foamy, honeycombed appearance 

Commonly used Stains: Giemsa, toluidine blue, methenamine silver, calcofluor white

Serology: measurement of 1-3 β-d-glucan levels, hypoxia, elevated LDH

Imaging: 

CXR: Diffuse, interstitial infiltration with classic “butterfly” pattern

CT Scan lung: bilateral patchy and ground-glass opacities and tree-in-bud nodular opacities

Treatment 

First-line therapeutic agent: Trimethoprim-sulfamethoxazole 

Other effective agents: Adjunctive corticosteroid therapy, Pentamidine, Clindamycin + Primaquine, dapsone, atovaquone