What is ICD-10 code B66.4?

B66.4 is the ICD-10-CM diagnosis code for Paragonimiasis. An infection caused by the Paragonimus parasitic worm, typically acquired by eating raw or undercooked freshwater crustaceans, affecting the lungs and sometimes the brain or other organs. B66.4 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. B66.4 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. B66.4 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. B66.4 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for B66.4?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. B66.4 was a payment HCC under V24 (Pneumococcal Pneumonia, Empyema, Lung Abscess) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting B66.4?

Document respiratory symptoms and whether pulmonary or extrapulmonary manifestations are present Note geographic exposure, as this infection is endemic to Asia, Africa, and South America Because B66.4 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

B66.4: Paragonimiasis — ICD-10 | Pneumococcal Pneumonia, Empyema, Lung Abscess

ICD-10-CM Code View

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Code lookupB66.4Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Helminthiases (B65-B83)

B66.4

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Paragonimiasis

An infection caused by the Paragonimus parasitic worm, typically acquired by eating raw or undercooked freshwater crustaceans, affecting the lungs and sometimes the brain or other organs.

Buddy Insight

Paragonimiasis is a parasitic lung infection caused by Paragonimus lung flukes, acquired by eating raw or undercooked freshwater crabs or crayfish.

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 115

Pneumococcal Pneumonia, Empye...

RAF 0.130

ACA/HHS

Mapped

HCC 163

HHS-HCC 163

Varies by metal level

ESRD/PACE

Mapped

HCC 115

Pneumococcal Pneumonia, Empye...

RAF 0.030

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

B66Other fluke infections

B66.4Paragonimiasis

Inclusion Terms

Official

Infection due to Paragonimus species
Lung fluke disease
Pulmonary distomiasis

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for B66.4 in this effective period.

Related Child Codes

Official

B66.0Opisthorchiasis

B66.1Clonorchiasis

B66.2Dicroceliasis

B66.3Fascioliasis

B66.5Fasciolopsiasis

Includes

Official

ICD-10-CM does not list Includes notes for B66.4 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for B66.4 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for B66.4 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for B66.4 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for B66.4 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Identification of Paragonimus eggs in sputum, stool, or pleural fluid

Positive Paragonimus serology (ELISA)

Chest imaging findings: infiltrates, nodules, cavitary lesions, pleural effusion

Dietary exposure history (raw freshwater crustaceans)

MEAT Support

HCC Buddy guidance

Identification of Paragonimus eggs in sputum, stool, or pleural fluid

Positive Paragonimus serology (ELISA)

Chest imaging findings: infiltrates, nodules, cavitary lesions, pleural effusion

Dietary exposure history (raw freshwater crustaceans)

Audit Caution

HCC Buddy guidance

Misdiagnosing as tuberculosis due to similar clinical and radiographic presentation — sputum examination for ova is key

Not recognizing paragonimiasis in patients from endemic areas presenting with chronic cough and hemoptysis

Coding only the pleural effusion or hemoptysis without the underlying parasitic infection

Missing extrapulmonary manifestations (cerebral paragonimiasis) that require additional codes

Common Mistakes

HCC Buddy guidance

A15.0 (Tuberculosis of lung) - paragonimiasis mimics pulmonary tuberculosis; ova identification differentiates

B67.1 (Echinococcus of lung) - different parasite (tapeworm vs fluke); different imaging pattern

J90 (Pleural effusion, not elsewhere classified) - if pleural effusion is from paragonimiasis, code the underlying infection

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is B66.4 an HCC code?

Yes. B66.4 maps to Pneumococcal Pneumonia, Empyema, Lung Abscess under the V24 model but is not retained in V28.

HCC Category Mapping

V24HCC 115, Pneumococcal Pneumonia, Empyema, Lung Abscess

0.130

ESRDHCC 115, Pneumococcal Pneumonia, Empyema, Lung Abscess

0.030

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work B66.4 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for B66.4

For B66.4to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed B66.4 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

B66.4 is the ICD-10-CM diagnosis code for paragonimiasis. An infection caused by the Paragonimus parasitic worm, typically acquired by eating raw or undercooked freshwater crustaceans, affecting the lungs and sometimes the brain or other organs. B66.4 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering helminthiases (b65-b83).

Under the older CMS-HCC V24 model, B66.4 maps to Pneumococcal Pneumonia, Empyema, Lung Abscess (HCC 115) with a community, non-dual, aged base RAF weight of 0.130. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Document respiratory symptoms and whether pulmonary or extrapulmonary manifestations are present. Because B66.4 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for B66.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Document respiratory symptoms and whether pulmonary or extrapulmonary manifestations are present
•Note geographic exposure, as this infection is endemic to Asia, Africa, and South America

Clinical Significance

Paragonimiasis is a parasitic lung infection caused by Paragonimus lung flukes, acquired by eating raw or undercooked freshwater crabs or crayfish. It can cause chronic cough with hemoptysis and pleural effusions, often mimicking tuberculosis in endemic areas. In the US, it is seen primarily in immigrants from Southeast Asia, West Africa, and Central/South America.

Documentation Requirements

✓Identification of Paragonimus eggs in sputum, stool, or pleural fluid
✓Positive Paragonimus serology (ELISA)
✓Chest imaging findings: infiltrates, nodules, cavitary lesions, pleural effusion
✓Dietary exposure history (raw freshwater crustaceans)
✓Geographic/immigration history from endemic region
✓Treatment documented (praziquantel)

Commonly Confused Codes

•A15.0 (Tuberculosis of lung) - paragonimiasis mimics pulmonary tuberculosis; ova identification differentiates
•B67.1 (Echinococcus of lung) - different parasite (tapeworm vs fluke); different imaging pattern
•J90 (Pleural effusion, not elsewhere classified) - if pleural effusion is from paragonimiasis, code the underlying infection