Cause: Most influenza infections are caused by influenza virus types A and B. Influenza A viruses are further classified into subtypes based on the hemagglutinin and neuraminidase proteins on the surface of the virus. Influenza A subtypes which are currently circulating include H1N1 and H3N2 viruses.
Illness and treatment: Symptoms of influenza generally include fever, cough, sore throat, muscle aches, headaches, and/or fatigue. Some people have no symptoms. Severe infections can cause shortness of breath and respiratory failure. Treatment with antiviral medication is recommended for persons with severe or progressive disease and persons at risk for severe disease.
Sources: Influenza virus is transmitted from person to person through respiratory secretions. Very rarely, influenza is transmitted from animals to humans.
Prevention: Vaccination with influenza vaccine is the best way to prevent the disease.
Recent Washington trends: Seasonal epidemics occur every year in Washington and the United States. Peak activity usually occurs between December and March.
Purpose of Reporting and Surveillance
- To assist healthcare providers with treatment decisions by tracking the geographic spread of influenza activity and determining the antiviral resistance patterns of circulating influenza strains.
- To estimate influenza-related mortality.
- To monitor the epidemiology of severe influenza infections.
- To collect influenza isolates for antigenic analysis and vaccine development. To detect emerging threats such as avian and other novel influenza strains.
Legal Reporting Requirements for Novel or Unsubtypable Influenza
- Health care providers and Health care facilities: immediately notifiable to local health jurisdiction
- Laboratories: immediately notifiable to local health jurisdiction; specimen submission required – isolate or if not available clinical specimen associated with positive result (2 business days)
- Veterinarians: suspected human cases immediately notifiable to local health jurisdiction; animal cases notifiable to Washington State Department of Agriculture (see: https://app.leg.wa.gov/WAC/default.aspx?cite=16-70)
- Local health jurisdictions: immediately notifiable to Washington State Department of Health (DOH) Communicable Disease Epidemiology Office
Legal Reporting Requirements for Influenza-associated Deaths (Laboratory-confirmed)
- Healthcare providers and Health care facilities: notifiable to local health jurisdiction within 3 business days
- Laboratories: no legal reporting requirement
- Local health jurisdictions: notifiable to Washington State Department of Health (DOH) Communicable Disease Epidemiology Office within 7 days of case investigation completion or summary information required within 21 days
Other Reporting Requirements
Healthcare providers and hospitals should also report the following to the local health jurisdiction where the patient resides:
- Outbreaks of influenza-like illness or lab-confirmed influenza in an institutional setting (e.g., long term care facility).
- Unexplained critical illness or death in persons
Case Definition - Novel Influenza (PDF)
Case Definition - Influenza-associated Death (PDF)
Influenza Death Reporting Form (PDF)
Pediatric Influenza Death Report Form (PDF)
Novel Influenza A Report Form (PDF)
Surveillance and Reporting Guideline - Novel Influenza (PDF)
Surveillance and Reporting Guideline - Influenza-associated Death (PDF)
Influenza Testing at PHL (PDF)