Diagnosing Influenza
While viral culture is the gold standard for confirming influenza infection and can distinguish between influenza A and B, diagnosis is often based on clinical presentation, especially when influenza viruses are circulating in the community. Testing for influenza is recommended when a patient is being admitted to the hospital or when results would influence management.
Depending on the type of diagnostic test used, the source of the specimen and the timeframe for expected results varies.
- Rapid influenza diagnostic tests (RIDTs): detect parts of the virus (antigen) that stimulate the immune response
- Nasopharyngeal swab, aspirate or wash; nasal swab, aspirate or wash; throat swab
- Results within 15 minutes
- Rapid molecular assays: detect genetic material of the virus
- Nasopharyngeal swab, nasal swab
- Results in 15 to 30 minutes
- Immunofluorescence assay
- Nasopharyngeal swab or wash; bronchial wash; nasal or endotracheal aspirate
- Results in two to four hours
- Viral culture
- Nasopharyngeal swab; throat swab; nasopharyngeal or bronchial wash; nasal or endotracheal aspirate; sputum
- Results in one to eight days
RIDTs and rapid molecular assays are more practical, producing results in less than an hour. However, they are not as accurate as the other methods and false negative results may occur.
Treating Influenza
Influenza infection is self-limited and varies in severity depending on vaccination status, age and comorbidities. Treatment for influenza is often symptomatic and includes rest, analgesics, hydration, and proper nutrition. Early antiviral treatment may shorten the duration of fever and other symptoms and may reduce the risk of complications.
Antiviral treatment is recommended within 48 hours of symptom onset for anyone who is hospitalized; anyone with severe, complicated, or progressive illness; and anyone at high risk for complications, including young children, adults aged 65 years and older, pregnant women, and people with certain chronic medical conditions.
The following medications are recommended for management of influenza:
- oral oseltamivir (Tamiflu®) – prevention and treatment in people 14 days and older
- inhaled zanamivir (Relenza®) – prevention and treatment in people 7 years and older
- intravenous peramivir (Rapivab®) – treatment only in people 2 years and older
- oral baloxavir marboxil (Xofluza®) – early treatment only in people 12 years and over; not recommended for pregnant women, breastfeeding mothers, outpatients with complicated or progressive illness, or hospitalized patients
Complications of flu can include bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions such as congestive heart failure, asthma, or diabetes.