2026 ICD-10-CM Diagnosis Code B66.1Clonorchiasis

ICD-10-CM Codes›A00–B99›B65-B83›B66

ICD-10-CM B66.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B66.1 is a billable ICD-10-CM diagnosis code for clonorchiasis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 441 through 443. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Parasitic, other specified and unspecified infections.

Code Identity

ICD-10-CM Code
B66.1
Billable Status
Yes — Valid for Submission
Code Describes
Clonorchiasis
Short Description
Clonorchiasis
Same as the full description in the CMS dataset.
Parent Code
B66
Other fluke infections

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB65-B83Helminthiases
CategoryB66Other fluke infections
This CodeB66.1Clonorchiasis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute clonorchiasis
  • Biliary cirrhosis
  • Chronic clonorchiasis
  • Clonorchiasis
  • Clonorchiasis with biliary cirrhosis
  • Fibrosis of bile duct
  • Infection of bile duct caused by parasite
  • Infectious cirrhosis
  • Opisthorchiasis
  • Parasitic cirrhosis

Tabular List NotesGuidance

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

Inclusion Terms

  • Chinese liver fluke disease
  • Infection due to Clonorchis sinensis
  • Oriental liver fluke disease

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.

    • Cholangiohepatitis
      • due to fluke infestation
    • Cirrhosis, cirrhotic(hepatic) (liver)
      • biliary (cholangiolitic) (cholangitic) (hypertrophic) (obstructive) (pericholangiolitic)
        • due to
          • Clonorchiasis
    • Clonorchiasis, clonorchis infection(liver)
    • Disease, diseased
      • Chinese liver fluke
    • Disease, diseased
      • liver (chronic) (organic)
        • fluke
          • Chinese
    • Disease, diseased
      • liver (chronic) (organic)
        • fluke
          • oriental
    • Disease, diseased
      • Oriental liver fluke
    • Distomiasis
      • hepatic
        • due to Clonorchis sinensis
    • Distomiasis
      • liver
        • due to Clonorchis sinensis
    • Infection, infected, infective(opportunistic)
      • Clonorchis (sinensis) (liver)
    • Infestation
      • Clonorchis (sinensis) (liver)
    • Infestation
      • fluke
        • liver (sheep)
          • Chinese
    • Infestation
      • fluke
        • liver (sheep)
          • due to clonorchiasis
    • Infestation
      • fluke
        • liver (sheep)
          • oriental

Clinical ClassificationClinical

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

CCSR INF009
Parasitic, other specified and unspecified infections
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Clonorchiasis

    infection of the biliary passages with clonorchis sinensis, also called opisthorchis sinensis. it may lead to inflammation of the biliary tract, proliferation of biliary epithelium, progressive portal fibrosis, and sometimes bile duct carcinoma. extension to the liver may lead to fatty changes and cirrhosis. (from dorland, 27th ed)

  • Opisthorchiasis

    infection with flukes of the genus opisthorchis.

  • Clonorchis sinensis

    a species of trematode flukes of the family opisthorchidae. many authorities consider this genus belonging to opisthorchis. it is common in china and other asiatic countries. snails and fish are the intermediate hosts.

  • Opisthorchiasis

    a parasitic disease caused by species of the genus opisthorchis. this infection with liver flukes is transmitted by eating raw or undercooked fish.

Patient EducationClinical

Parasitic Diseases

Parasites are living things that use other living things - like your body - for food and a place to live. You can get them from contaminated food or water, a bug bite, or sexual contact. Some parasitic diseases are easily treated and some are not.

Read the full article at MedlinePlus

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

Convert B66.1 to ICD-9-CMHistory

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

ICD-9-CM
121.1 Clonorchiasis
Exact Match The mapping is direct, with no qualifiers.

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 B66.1Overview

Is B66.1 (Other fluke infections) a billable code?

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

What MS-DRG does B66.1 group to?

When clonorchiasis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 441, 442, 443, with relative weights from 0.6997 to 1.7947 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of B66.1?

Under the General Equivalence Mappings, clonorchiasis converts to ICD-9-CM 121.1 (clonorchiasis). The mapping is a direct match.

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.