ICD-10 Code B99 – Other and unspecified infectious diseases (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B99 – Other and unspecified infectious diseases
What it is
B99 is a diagnosis code for infectious diseases that are documented but not named more specifically. Use it when the record confirms an infection, yet the provider does not identify a precise organism or site.
Clinical signs
Clinical features vary; refer to documentation. Records may describe nonspecific infectious illness, fever, inflammation, or a confirmed infection without enough detail to assign a more exact code.
When to use this code
Use B99 when the provider clearly documents an infectious disease and no more specific ICD-10-CM code is supported. It may fit cases where the organism, site, or type is not stated in the note. If later documentation identifies the condition more precisely, code the specific infection instead.
Do not use for
Do not use B99 when a more specific infectious disease code is documented or can be supported from the record. Do not use it for suspected infection without confirmation; check documentation.
Coding tip
Review the note for organism, site, and type before assigning B99, because a more specific code usually takes priority.