2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B33.1 is a billable ICD-10-CM diagnosis code for Ross River disease. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) 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

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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B33.1: its own notes plus those printed at Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Epidemic polyarthritis and exanthema
  • Ross River fever

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name B33.1, its category, or a range that includes it.

Applicable To 1

These notes mention B33.1.

  • O98.5 Other viral diseases complicating pregnancy, childbirth and the puerperium
    Conditions in A80-B09, B25-B34, R87.81-, R87.82- names B25-B34, which includes this code

Excludes1 1

These codes carry an Excludes1 note naming B33.1: they are not reported together with it, unless the two conditions are unrelated.

  • A92 Other mosquito-borne viral fevers
    Ross River disease (B33.1)

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 866, 865, with relative weights from 0.8691 to 1.3153 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 2027. 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.