Influenza

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Influenza

Definition

  • Acute respiratory disease caused by influenza virus (Influenza virus A/B/C/D) infection

Causative pathogen

  • Influenza virus A/B/C/D

Transmission route

  • Droplet transmission

Common targets

  • Occurs in all age groups

Incubation period and contagious period

  • 1 to 4 days (average 2 days)
  • From 1 day before the onset of symptoms to 5 to 7 days after onset * However, in children or immunocompromised individuals, the virus shedding period may extend beyond 10 days.

Clinical symptoms

  • High fever (38 to 40℃), respiratory symptoms such as dry cough and sore throat, as well as general symptoms like headache, muscle pain, fatigue, weakness, and loss of appetite
  • Accompanied by runny nose, nasal congestion, eye pain, vomiting, and abdominal pain

Treatment

  • Symptomatic treatment
  • Antiviral treatment

Prevention

  • Vaccination
  • Proper handwashing and adherence to cough etiquette
  • Avoidance of touching eyes, nose, and mouth with unwashed hands
  • During the symptomatic period, limiting visits to workplaces, schools, and public places, and resting at home

Diagnosis/Reporting criteria

  • Reporting scope: Patients, suspected cases
    • (Patient) A person who shows clinical symptoms consistent with influenza and is confirmed to be infected with the infectious pathogen according to diagnostic criteria
    • (Suspected case) A person showing fever above 38℃ along with cough or sore throat
  • Diagnostic criteria: Detection of specific genes in the specimen
  • Reporting period: Report within 7 days
  • Responsible department
    • (Reporting) Division of Infectious Disease Control
    • (Diagnosis) Division of Emerging Infectious Diseases

Clinical Surveillance of Influenza-like Illness (ILI)

Case definition

  • Influenza patient
    • A person who shows clinical symptoms consistent with influenza and is confirmed to be infected with the infectious pathogen according to diagnostic criteria
  • Influenza-like illness (ILI)
    • A person showing fever above 38°C along with cough or sore throat

Objective

  • Continuous monitoring of trends in the occurrence of influenza-like illness to identify outbreaks early
  • Provision of foundational data for establishing national influenza control measures

Designation of sentinel surveillance sites

  • 300 outpatient institutions nationwide (pediatrics, internal medicine, family medicine, otorhinolaryngology)
    • Weekly surveillance (status reports of influenza-like illness patients among those treated from Sunday to Saturday within 7 days)
  • Influenza sentinel surveillance (clinical) flowchart
  • Korea Disease Control and Prevention Agency
    • Designation of sentinel surveillance sites
    • Analysis of surveillance data and information feedback
  • City/Province
    • Confirming and preparing for influenza outbreak situations Distribution of feedback materials, etc.
    • Distribution of feedback materials, etc.
  • City/County/District Health Center
    • Management of sentinel surveillance sites
    • Distribution of feedback materials, etc.
  • Sentinel surveillance institution
    • Report the total number of patients treated and the number of influenza-like illness patients to the Korea Disease Control and Prevention Agency
  • Receipt of reporting data Feedback of analysis data
  • Feedback of analysis data Report

Outbreak criteria

  • 2024-2025 influenza season outbreak criteria ⌜8.6 cases per 1,000 outpatient visits
  • Before the start of each season (September to the following August), expert advisory meetings will be held to establish outbreak criteria, and an influenza outbreak warning will be issued if the criteria are exceeded. * During an outbreak warning period, antiviral medications are prescribed based on suspected symptoms alone for high-risk groups for influenza (children, pregnant women or mothers within 2 weeks of childbirth, individuals over 65 years old, immunocompromised individuals, and those with underlying conditions) without separate testing, with health insurance coverage applied.

Incidence rate of influenza-like illness patients by solar term (solar term No. 19-20 to solar term No. 24-25)

graph

Monitoring of Influenza-related Hospitalizations and Deaths

Definition of reporting criteria terminology

  • Total influenza patients
    • New hospitalized patients, outpatients, and emergency room visits diagnosed with influenza
  • Influenza outpatients
    • New outpatients and emergency room patients diagnosed with influenza
  • Influenza-related deaths
    • Among the death cases at sentinel surveillance sites, those who received a confirmed influenza diagnosis within 30 days before death

Objective

  • Monitor hospitalizations and deaths due to influenza each season to assess severity

Designation of sentinel surveillance sites

  • Sentinel surveillance medical institutions for acute respiratory infections * Designation criteria: Public hospitals and medical institutions with 200 or more beds, and tertiary care hospitals
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