Influenza infection is characterized by upper and lower respiratory tract symptoms of rhinorrhea, cough, fever, chills, headache, and myalgia.
Typically presents in winter season.
Can occur in local community outbreaks, epidemics, and, rarely, pandemics.
Vaccination for prevention is available.
Antiviral treatment is recommended for people at high risk of developing complications of influenza, and should be started within 48 hours of onset of symptoms.
Acute respiratory tract infection typically caused by influenza A or B virus. The virus is transmitted by inhalation of infected respiratory secretions that have been aerosolized through coughing, sneezing, or talking.
History and exam
Key diagnostic factors
- winter season
- current influenza outbreak
- fever with cough
Other diagnostic factors
- sore throat
- cervical lymphadenopathy
- age ≥65 years
- age 6-59 months
- chronic cardiovascular or respiratory conditions
- chronic kidney disease (CKD)
- caregivers and household contacts of high-risk groups
- healthcare workers
1st investigations to order
- clinical diagnosis
Investigations to consider
- molecular assays
- antigen detection tests
- viral culture
- chest x-ray
exposure to infected individual(s) in at-risk population
- Coronavirus disease 2019 (COVID-19)
- Bacterial pneumonia
- Rhinovirus infection
- Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2023-24 influenza season
- Canadian immunization guide chapter on influenza and statement on seasonal influenza vaccine for 2022-2023
Antibiotics: what you need to knowMore Patient leaflets
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