B59
Pneumocystosis
B59 is a billable ICD-10-CM diagnosis code for pneumocystosis. It is part of the FY2027 code set, effective October 1, 2026. The Alphabetic Index lists it under 10 entries. Its coding notes include a Use additional code instruction, 2 Excludes1 entries and 5 Excludes2 entries.
Use additional code
Add the listed code as a secondary code, if known.
Excludes1
Not coded here. The listed conditions generally should not be reported together.
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
Also from chapter/block level (5 notes)
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Care settings
How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.
Home Health Primary
Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the MMTA - Infectious Disease, Neoplasms, and Blood-Forming Diseases clinical group.
Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026Hospital MCC
Counts as a major complication or comorbidity (MCC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 105 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.
Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix CIncludes
Further defines or gives examples of the content of the category.
Also from chapter/block level (1 note)
- diseases generally recognized as communicable or transmissible
Inclusion terms
Conditions classified to this code.
- Pneumonia due to Pneumocystis carinii
- Pneumonia due to Pneumocystis jirovecii
Alphabetic Index terms
Terms the official Alphabetic Index lists for this code. 10 entries
- Disease, diseased, protozoal, pneumocystosis
- Infection, infected, infective (opportunistic), Pneumocystis carinii (pneumonia)
- Infection, infected, infective (opportunistic), Pneumocystis jirovecii (pneumonia)
- Pneumocystis carinii pneumonia
- Pneumocystis jirovecii (pneumonia)
- Pneumocystosis (with pneumonia)
- Pneumonia (acute) (double) (migratory) (purulent) (septic) (unresolved), in (due to), pneumocystosis (Pneumocystis carinii) (Pneumocystis jirovecii)
- Pneumonia (acute) (double) (migratory) (purulent) (septic) (unresolved), interstitial, plasma cell
- Pneumonia (acute) (double) (migratory) (purulent) (septic) (unresolved), plasma cell (of infants)
- Pneumonia (acute) (double) (migratory) (purulent) (septic) (unresolved), Pneumocystis (carinii) (jirovecii)