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Influenza infection

Last reviewed: 13 Oct 2025
Last updated: 19 Aug 2025

Summary

Definition

History and exam

Key diagnostic factors

  • winter season
  • current influenza outbreak
  • unvaccinated
  • fever with cough
Full details

Other diagnostic factors

  • sore throat
  • cervical lymphadenopathy
  • dyspnea
Full details

Risk factors

  • age ≥65 years
  • age 6-59 months
  • chronic cardiovascular or respiratory conditions
  • diabetes
  • hemoglobinopathy
  • immunocompromised status
  • chronic kidney disease (CKD)
  • pregnancy
  • caregivers and household contacts of high-risk groups
  • healthcare workers
Full details

Diagnostic investigations

1st investigations to order

  • clinical diagnosis
Full details

Tests to avoid

  • broad respiratory pathogen panels
  • serology
Full details

Investigations to consider

  • molecular assays
  • antigen detection tests
  • viral culture
  • chest x-ray
Full details

Treatment algorithm

INITIAL

exposure to infected individual(s) in at-risk population

ACUTE

adults

children

Contributors

Authors

Kyle Eggleton, MBChB PhD FRNZCGP(Dist)

Associate Dean Rural

Department of General Practice and Primary Health Care

University of Auckland

Auckland

New Zealand

Disclosures

KE declares that he has no competing interests.

Rachel Roskvist, MBChB, FRNZCGP, MHSc

Senior Lecturer

Department of General Practice and Primary Health Care

University of Auckland

Auckland

New Zealand

Disclosures

RR declares that she has no competing interests.

Bruce Arroll, MBChB PhD FRNZCGP

Department of General Practice and Primary Health Care

University of Auckland

Auckland

New Zealand

Disclosures

BA declares that he has no competing interests.

Acknowledgements

Dr Kyle Eggleton, Dr Rachel Roskvist, and Professor Bruce Arroll would like to gratefully acknowledge Dr Cristine Radojicic, a previous contributor to this topic.

Disclosures

CR declares that she is on Advisory boards for CSL Behring and Speakers Bureau Biocryst.

Revisores por pares

Michael Ison, MD

Chief

Respiratory Diseases Branch

National Institute of Allergy and Infectious Diseases

Bethesda

MD

Divulgaciones

MI declares that he has no competing interests.

Waleed Javaid, MD, FACP, FIDSA

Associate Professor

Medical Director of Infection Control

Infectious Disease

Department of Medicine

SUNY Upstate Medical University

Syracuse

NY

Divulgaciones

WJ declares that he has no competing interests.

Rachel L. Miller, MD, FAAAAI

Associate Professor of Clinical Medicine and Environmental Health Sciences

Columbia University College of Physicians and Surgeons

New York

NY

Divulgaciones

RLM declares that she has no competing interests.

Mark Sands, MD, FAAAAI

Chief

SUNY Buffalo School of Medicine

Division Allergy and Immunology

Buffalo

NY

Divulgaciones

MS declares that he has no competing interests.

An De Sutter, MD, PhD

Associate Professor

Department of General Practice and Primary Health Care

Ghent University

Ghent

Belgium

Divulgaciones

ADS declares that she has no competing interests.

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Referencias

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Artículos principales

Uyeki TM, Bernstein HH, Bradley JS, et al. Clinical practice guidelines by the Infectious Diseases Society of America: 2018 update on diagnosis, treatment, chemoprophylaxis, and institutional outbreak management of seasonal influenza. Clin Infect Dis. 2019 Mar 5;68(6):e1-47.Texto completo  Resumen

Centers for Disease Control and Prevention. Influenza (flu). Feb 2024 [internet publication].Texto completo

Centers for Disease Control and Prevention. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2024-25 Influenza Season. Aug 2024 [internet publication].Texto completo  Resumen

Centers for Disease Control and Prevention. ​Child and adolescent immunization schedule by age (addendum updated July 2, 2025): recommendations for ages 18 years or younger, United States, 2025. Jul 2025 [internet publication].Texto completo

Centers for Disease Control and Prevention. Adult immunization schedule by age (addendum updated July 2, 2025): recommendations for ages 19 years or older, United States, 2025. Jul 2025 [internet publication].Texto completo

Centers for Disease Control and Prevention. Influenza antiviral medications: summary for clinicians. Dec 2023 [internet publication].Texto completo

Artículos de referencia

Una lista completa de las fuentes a las que se hace referencia en este tema está disponible para los usuarios con acceso a todo BMJ Best Practice.
  • Diferenciales

    • Coronavirus disease 2019 (COVID-19)
    • Bacterial pneumonia
    • Rhinovirus infection
    Más Diferenciales
  • Guías de práctica clínica

    • Statement on seasonal influenza vaccines for 2025-2026
    • Child and adolescent immunization schedule by age: recommendations for ages 18 years of younger, United States, 2025
    Más Guías de práctica clínica
  • Folletos para el paciente

    Flu

    Antibiotics: what you need to know

    Más Folletos para el paciente
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