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ICD-10-CM 2027 diagnosis code

B66.9Fluke infection, unspecified

✓ Billable / specific

B66.9 is a valid, billable ICD-10-CM code for fluke infection, unspecified. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About B66.9

B66.9 is the ICD-10-CM diagnosis code for fluke infection, unspecified. It belongs to category B66 (other fluke infections), block B65-B83 (helminthiases) and chapter 1 (certain infectious and parasitic diseases). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within B66, choose B66.9 (Fluke infection, unspecified) only when documentation doesn't support a more specific option: Opisthorchiasis (B66.0), Clonorchiasis (B66.1), Dicroceliasis (B66.2), Fascioliasis (B66.3), Paragonimiasis (B66.4), Fasciolopsiasis (B66.5) and other specified fluke infections (B66.8).

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.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 121.9 (trematode infection, unspecified).

Notes that apply from higher levels

Instructions written at a parent level also apply to B66.9.

Broader instructions also apply from Chapter 1: Certain infectious and parasitic diseases.

Alphabetic index entries

2 entries

Terms in the official ICD-10-CM index that lead to B66.9.

MS-DRG v44.0 grouping

All DRGs →

Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.

ICD-9-CM equivalent

Converter →
  • 121.9Trematode infection, unspecifiedexact

From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about B66.9

Is B66.9 billable?

Yes. B66.9 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can B66.9 be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict B66.9 as a principal diagnosis.

Is B66.9 a CC or MCC?

No. B66.9 is neither a CC nor an MCC under MS-DRG v44.0.

What DRG does B66.9 group to?

B66.9 is used in the MS-DRG v44.0 logic for MS-DRG 867 (Other Infectious and Parasitic Diseases Diagnoses with MCC), MS-DRG 868 (Other Infectious and Parasitic Diseases Diagnoses with CC) and MS-DRG 869 (Other Infectious and Parasitic Diseases Diagnoses without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.

What is the ICD-9 code for B66.9?

The CMS General Equivalence Mappings map B66.9 to ICD-9-CM 121.9.