B99.9 Unspecified infectious disease

The ICD-10-CM code for Unspecified infectious disease is B99.9 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

1: Certain infectious and parasitic diseases (A00-B99)

Section

B99: Other infectious diseases (B99)

Category B99

3 codes (2 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to B99.9:

• Infection, infected, infective (opportunistic)
• Disease, diseased › epidemic
• Fever (inanition) (of unknown origin) (persistent) (with chills) (with rigor) › infective
• Granuloma › infectious
• Disease, diseased › infectious, infective

U.S. Hospital Utilization

• An estimated 2,570 U.S. inpatient stays in 2023 included B99.9 among the documented diagnoses.
• 325 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

HIV Infections (TOC entry)

a. Human Immunodeficiency Virus (HIV) Infections .............................................................. 19

Infectious agents causing diseases in other chapters (TOC)

b. Infectious agents as the cause of diseases classified to other chapters ................................. 22

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)