B59 Pneumocystosis

The ICD-10-CM code for Pneumocystosis is B59 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

1: Certain infectious and parasitic diseases (A00-B99)

Section

B50-B64: Protozoal diseases (B50-B64)

Category B59

1 code (1 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to B59:

• Pneumocystosis (with pneumonia)
• Pneumocystis carinii pneumonia
• Pneumocystis jirovecii (pneumonia)
• Pneumonia (acute) (double) (migratory) (purulent) (septic) (unresolved) › Pneumocystis (carinii) (jirovecii)
• Infection, infected, infective (opportunistic) › Pneumocystis jirovecii (pneumonia)
• Pneumonia (acute) (double) (migratory) (purulent) (septic) (unresolved) › plasma cell (of infants)
• Infection, infected, infective (opportunistic) › Pneumocystis carinii (pneumonia)
• Disease, diseased › protozoal › pneumocystosis

Inclusion Terms

• Pneumonia due to Pneumocystis carinii
• Pneumonia due to Pneumocystis jirovecii

U.S. Hospital Utilization

• An estimated 10,535 U.S. inpatient stays in 2023 included B59 among the documented diagnoses.
• 1,710 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

HIV Infections (TOC entry)

a. Human Immunodeficiency Virus (HIV) Infections .............................................................. 19

Infectious agents causing diseases in other chapters (TOC)

b. Infectious agents as the cause of diseases classified to other chapters ................................. 22

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)