2026 ICD-10-CM Diagnosis Code B33.1Ross River disease

ICD-10-CM Codes›A00–B99›B25-B34›B33

ICD-10-CM B33.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B33.1 is a billable ICD-10-CM diagnosis code for Ross River disease. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 865 through 866. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B33.1
Billable Status
Yes — Valid for Submission
Code Describes
Ross River disease
Short Description
Ross River disease
Same as the full description in the CMS dataset.
Parent Code
B33
Other viral diseases, not elsewhere classified

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB25-B34Other viral diseases
CategoryB33Other viral diseases, not elsewhere classified
This CodeB33.1Ross River disease

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Ross River disease

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Epidemic polyarthritis and exanthema
  • Ross River fever

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Disease, diseased
      • Ross River
    • Fever(inanition) (of unknown origin) (persistent) (with chills) (with rigor)
      • Ross River
    • Polyarthritis, polyarthropathy
      • epidemic (Australian) (with exanthema)
    • Ross River disease or fever

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INF008
Viral infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Viral Infections

Viruses are very tiny germs. They are made of genetic material (either DNA or RNA) inside of a protein coating. There are a huge number of viruses on earth. Only a small number of them can infect humans. Those viruses can infect our cells, which may cause disease.

The full article covers:

  • What are viruses?
  • How are viruses spread?
  • How do viruses cause disease?
  • What are the treatments for viral infections?
  • Can viral infections be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert B33.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
066.3 Mosquito-borne fever NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About B33.1Overview

Is B33.1 (Other viral diseases, not elsewhere classified) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report Ross River disease on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does B33.1 group to?

When Ross River disease is the principal diagnosis on an inpatient stay, it groups to MS-DRG 865, 866, with relative weights from 0.8696 to 1.4983 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of B33.1?

Under the General Equivalence Mappings, Ross River disease converts to ICD-9-CM 066.3 (mosquito-borne fever NEC). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.