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ICD-10 Guide
ICD-10 CodesA85.2

A85.2

Eastern equine encephalitis

BILLABLE STATUSYes
IMPLEMENTATION DATEOctober 1, 2015
LAST UPDATED09/05/2025

Code Description

ICD-10 A85.2 is a billable code used to indicate a diagnosis of eastern equine encephalitis.

Key Diagnostic Point:

Eastern equine encephalitis (EEE) is a rare but serious viral infection that affects the central nervous system (CNS), primarily caused by the Eastern equine encephalitis virus (EEEV). This virus is transmitted to humans through the bite of infected mosquitoes, particularly in areas near marshes and wetlands. The clinical presentation of EEE can range from mild flu-like symptoms to severe neurological complications, including encephalitis, seizures, and coma. Patients may experience high fever, headache, and altered mental status, with rapid progression to neurological deficits. The mortality rate for EEE is significant, with approximately 30% of infected individuals succumbing to the disease, and many survivors may suffer from long-term neurological sequelae. Vaccination against EEE is available for horses and is recommended in endemic areas, but there is currently no specific vaccine for humans. Early diagnosis and supportive care are crucial for improving outcomes in affected individuals.

Code Complexity Analysis

Complexity Rating: Medium

Medium Complexity

Complexity Factors

  • Variability in clinical presentation and severity of symptoms.
  • Need for accurate documentation of exposure history and symptom onset.
  • Differentiation from other viral encephalitides and CNS infections.
  • Potential for co-infection with other mosquito-borne viruses.

Audit Risk Factors

  • Inadequate documentation of mosquito exposure.
  • Failure to document neurological assessments.
  • Misclassification of EEE as a less severe viral infection.
  • Lack of clarity on vaccination status and its relevance.

Specialty Focus

Medical Specialties

Infectious Disease

Documentation Requirements

Thorough documentation of travel history, exposure to mosquitoes, and symptom onset.

Common Clinical Scenarios

Patients presenting with fever, headache, and neurological symptoms after residing in or visiting endemic areas.

Billing Considerations

Consideration of differential diagnoses and the need for laboratory confirmation of EEE.

Neurology

Documentation Requirements

Detailed neurological examination findings, imaging results, and treatment plans.

Common Clinical Scenarios

Patients with acute encephalitis symptoms requiring neurological evaluation.

Billing Considerations

Documentation of long-term neurological outcomes and rehabilitation needs.

Coding Guidelines

Inclusion Criteria

Use A85.2 When
  • According to the official coding guidelines, A85
  • 2 should be used when there is a confirmed diagnosis of Eastern equine encephalitis, supported by clinical findings and laboratory confirmation
  • infection is documented

Exclusion Criteria

Do NOT use A85.2 When
  • Exclusion criteria include other viral encephalitides unless co

Related CPT Codes

87491CPT Code

Viral detection by nucleic acid (DNA or RNA) probe technique.

Clinical Scenario

Used for confirming EEE diagnosis through laboratory testing.

Documentation Requirements

Document the need for viral testing based on clinical presentation.

Specialty Considerations

Infectious disease specialists may require additional lab results for comprehensive evaluation.

ICD-10 Impact

Diagnostic & Documentation Impact

Enhanced Specificity

ICD-10 Improvements

The transition to ICD-10 has allowed for more specific coding of EEE, improving the accuracy of epidemiological tracking and resource allocation for public health initiatives.

ICD-9 vs ICD-10

The transition to ICD-10 has allowed for more specific coding of EEE, improving the accuracy of epidemiological tracking and resource allocation for public health initiatives.

Reimbursement & Billing Impact

reimbursement.

Resources

Clinical References

  • •
    CDC Eastern Equine Encephalitis Information

Coding & Billing References

  • •
    CDC Eastern Equine Encephalitis Information

Frequently Asked Questions

What are the common symptoms of Eastern equine encephalitis?

Common symptoms include fever, headache, confusion, seizures, and in severe cases, coma. Symptoms can develop rapidly after infection.

Is there a vaccine for Eastern equine encephalitis in humans?

Currently, there is no vaccine for humans. Vaccination is available for horses, which helps reduce the risk of transmission to humans.