Pneumocystis jirovecii Pneumonia Classification

Organism Classification

• The Centers for Disease Control and Prevention, as reflected in MMWR Recommendations and Reports, classifies Pneumocystis jirovecii as a fungus based on DNA analysis and cell wall composition, which is a critical distinction for diagnostic and therapeutic approaches 1, 2, 4
• DNA sequencing and cell wall composition analysis demonstrate that P. jirovecii belongs to the fungus kingdom, despite sharing some biological features with protozoa, as noted by the Kidney International journal 1
• The organism cannot be cultured in routine microbiology laboratories, which is an important practical limitation distinguishing it from many other fungi, according to Kidney International 1, 2
• Taxonomic nomenclature has evolved: the organism affecting humans is specifically named Pneumocystis jirovecii, while P. carinii refers only to the organism found in rats, as stated in MMWR Recommendations and Reports 4

Clinical Implications of Fungal Classification

• The European Society of Clinical Microbiology and Infectious Diseases recommends diagnostic testing including fungal-specific markers such as β-D-glucan (BDG), which is a component of fungal cell walls and can aid in PCP diagnosis 5
• The Infectious Diseases Society of America groups the organism with other pulmonary invasive fungal infections (pIFI) in clinical guidelines for immunocompromised patients, particularly those with hematological malignancies, as noted in Clinical Microbiology and Infection 5, 7