ICD-10 Code B59 – Pneumocystosis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B59 – Pneumocystosis
What it is
B59 identifies pneumocystosis, an infection caused by Pneumocystis jirovecii. It is most often documented as Pneumocystis pneumonia, especially in patients with weakened immune systems.
Clinical signs
Typical findings include progressive shortness of breath, cough, and fever. Clinical features vary; refer to documentation, especially when imaging or other notes support Pneumocystis infection.
When to use this code
Use B59 when the provider documents pneumocystosis, Pneumocystis jirovecii infection, or Pneumocystis pneumonia. Code it when the diagnosis is confirmed or clearly stated in the record. If the chart only suggests an opportunistic infection without naming Pneumocystis, check documentation.
Do not use for
Do not use B59 for nonspecific pneumonia, fungal infection not identified as Pneumocystis, or colonization without disease. If the record is unclear, check documentation.
Coding tip
Capture the exact organism and site wording from the provider note, because “Pneumocystis” documentation supports B59 more clearly than generic pneumonia terms.