ICD-10-CM 2027
ICD-10 code for infective fever
From the official ICD-10-CM alphabetic index entry “Fever (inanition) (of unknown origin) (persistent) (with chills) (with rigor) › infective”. Page updated September 29, 2026.
About coding infective fever
The ICD-10-CM code for infective fever is B99.9 (Unspecified infectious disease). The official index lists 1 more specific code, so check the documentation for details such as type, cause, site or severity before settling on B99.9.
Within B99, choose B99.9 (Unspecified infectious disease) only when documentation doesn't support a more specific option: other infectious disease (B99.8).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
In MS-DRG v44.0, it is part of the grouping logic for DRG 867 (Other Infectious and Parasitic Diseases Diagnoses with MCC, relative weight 2.1859), DRG 868 (Other Infectious and Parasitic Diseases Diagnoses with CC, relative weight 1.0235) and DRG 869 (Other Infectious and Parasitic Diseases Diagnoses without CC/MCC, relative weight 0.6787), in MDC 18 (Infectious and Parasitic Diseases, Systemic or Unspecified Sites), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
More specific infective fever codes (official index)
- specified NEC B99.8 — Other infectious disease
Common questions about infective fever ICD-10 codes
What is the ICD-10 code for infective fever?
- B99.9 — Unspecified infectious disease. More specific codes apply when the documentation supports them: B99.8.
Is B99.9 billable?
- Yes. B99.9 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can B99.9 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict B99.9 as a principal diagnosis.
Is B99.9 a CC or MCC?
- No. B99.9 is neither a CC nor an MCC under MS-DRG v44.0.