2026 ICD-10-CM Diagnosis Code B33.1Ross River disease
ICD-10-CM Codes›A00–B99›B25-B34›B33
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Not Chronic
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. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 186 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.
Code Identity
Code Classification
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
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Disease, diseased See Also: Syndrome;
Ross River B33.1
Fever (inanition) (of unknown origin) (persistent) (with chills) (with rigor) R50.9
Ross River B33.1
Polyarthritis, polyarthropathy See Also: Arthritis; M13.0
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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.
Code HistoryHistory
Questions About B33.1Overview
What is the ICD-10 code for Ross River disease?
The ICD-10-CM code for Ross River disease is B33.1 (sometimes written as B331). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
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.
Is B33.1 a CC or MCC?
CMS lists B33.1 as a CC (complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 186 closely related codes in its exclusion list.
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.
