ICD-10 Code B99.9 – Unspecified infectious disease (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B99.9 – Unspecified infectious disease
What it is
B99.9 identifies an infectious disease when the record does not specify the organism or the exact infection. Use it only when documentation confirms an infection, but the type is not further defined.
Clinical signs
Clinical features vary; refer to documentation. Records may note signs of infection such as fever, localized inflammation, or a nonspecific infectious process, but the source or organism is not identified.
When to use this code
Use B99.9 when the clinician documents an infectious disease without naming the causative agent or a more specific diagnosis. It may fit discharge summaries, problem lists, or referrals where the infection is confirmed but remains unspecified.
You should code to a more specific infectious diagnosis when the chart supports it. If the note is unclear, check documentation before assigning this code.
Do not use for
Do not use B99.9 for suspected infection, colonization, or noninfectious inflammatory conditions. It is also incorrect when a more specific infectious code is documented or can be determined from the record.
Coding tip
If the provider names only “infection” or “infectious disease,” query for clarification before defaulting to B99.9.