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    Last Updated Oct 05, 2023
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    • Influenza is common and causes a significant burden of disease in the ED.
    • Average of 12,200 hospitalizations and 3,500 deaths per year in Canada (1–3).
    • Multiple strains of Influenza A and B virus mutate from season to season.
    • Influenza A is the most common and most likely to cause epidemics.
    • Transmitted by respiratory secretions – droplet and contact precautions.

    Source: Provincial Infection Control Network of BC

    Clinical Presentation

    • World Health Organization defines Influenza-like illness (ILI) as: “An acute respiratory illness with a measured temperature of ≥ 38 °C and cough, with onset within the past 10 days” (5).
    • Other typical symptoms include headache, myalgias, malaise, sore throat, rhinorrhea, weakness, dizziness and anorexia.
    • Incubation: 18-72 hours.
    • Duration 2-5 days; can last more than 1 week.
    • Viral shedding 7 days; prolonged in children and immunocompromised.


    • Pneumonia (bacterial or viral)
      • NB Community-Acquired – MRSA pneumonia – usually severe.
    • Sepsis can be caused by influenza or secondary bacterial infection
      • Consider treatment for sepsis if clinically suspected, signs of organ failure, unclear diagnosis.
    • Myositis, rhabdomyolysis
    • Myocardial infarction, pericarditis, myocarditis
    • Encephalitis, aseptic meningitis
    • Guillain-Barré Syndrome
    • Toxic shock syndrome (Usually Staph aureus).



    • Droplet and contact precautions.

    Personal protective equipment

    Supportive management

    • Acetaminophen and NSAIDs if no contraindications
    • Hydration
    • Oxygen as needed.

    Specific treatments

    • Lung protective ventilation for acute respiratory distress syndrome (ARDS)
    • Antibiotics for pneumonia, sepsis, Toxic Shock syndrome
    • Antiviral medications (Oseltamivir).


    • Consider antivirals in any patient with ILI and symptoms < 48 hours and negative COVID testing.
    • Strongly consider treatment regardless of symptom duration of patients with:
      • severe influenza (ARDS, pneumonia, hospitalized, cardiac or CNS involvement)
      • high risk for severe influenza (Appendix 2).
    • Antiviral medications:
      • Oseltamivir (Tamiflu) is currently the only option
      • Baloxavir marboxil is not yet approved in Canada
      • Amantadine is not recommended due to high incidence of resistance.


    • Routine testing for influenza is not indicated.
    • Clinical diagnosis is as reliable as laboratory testing for influenza (9).
    • Test:
      • Patients with severe disease (hospital or ICU admission)
      • Unclear diagnosis when testing may decrease antibiotic use or alter further workup
    • Most routine testing for influenza in BC is by the viral nasopharyngeal swab (image).
    • Nasopharyngeal Swab Video.


    • Vaccination is the best way
    • Hand hygiene
    • Respiratory (droplet) precautions

    Influenza Vaccination

    • Free in BC to high risk people and those in close contact with high risk people (majority of the population)
    • Inactivated Influenza (Flu) Vaccine – HealthLink BC
    • Offer a flu shot to unvaccinated ED patients as we found 83% were found to be at high risk of influenza complications at Vancouver General Hospital (10)

    Related Information

    Reference List

    1. Zhao L, Young K, Gemmill I. Summary of the NACI Seasonal Influenza Vaccine Statement for 2019–2020. Canada Commun Dis Rep. 2019;45(6):149–55.

    2. Schanzer DL, Mcgeer A, Morris K. Statistical estimates of respiratory admissions attributable to seasonal and pandemic influenza for Canada. Influenza Other Respi Viruses. 2013;7(5):799–808.

    3. Schanzer DL, Sevenhuysen C, Winchester B, Mersereau T. Estimating influenza deaths in Canada, 1992-2009. PLoS One. 2013;8(11).

    4. Dolin R, Hirsch M, Thorner A. Clinical manifestations of seasonal influenza in adults – UpToDate [Internet]. [cited 2019 Nov 1]. 



    5. Fitzner J, Qasmieh S, Mounts AW, Alexander B, Besselaar T, Briand S, et al. Revision of clinical case definitions: Influenza-like illness and severe acute respiratory infection. Bull World Health Organ. 2018;96(2):122–8.

    6. Aoki FY, Allen UD, Stiver HG, Evans GA. The use of antiviral drugs for influenza: A foundation document for practitioners. Can J Infect Dis Med Microbiol. 2013;24(3):1–15.

    7. Giwa AL, Ogedegbe C, Murphy CG. Influenza: diagnosis and management in the emergency department. Emerg Med Pract. 2018;20(12):1–20.

    8. Stiver HG, Aoki FY, Allen UD, Evans GA, Laverdière M, Skowronski DM. Update on influenza antiviral drug treatment and prophylaxis for the 2015–2016 influenza season. Off J Assoc Med Microbiol Infect Dis Canada. 2016;1(1):1–4.

    9. Stein J, Louie J, Flanders S, Maselli J, Hacker JK, Drew WL, et al. Performance characteristics of clinical diagnosis, a clinical decision rule, and a rapid influenza test in the detection of influenza infection in a community sample of adults. Ann Emerg Med. 2005;46(5):412–9.

    10. Taylor JA, Vu E, Leon Elizalde MA, Li-Brubacher J. Influenza and pneumococcal disease vaccinations: Is there a role for prevention in the emergency department? BC Med J. 2018;60(2):116–20.

    Relevant Resources


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    Nasopharyngeal Swab

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    Sepsis and Soft Tissue Infections


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