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.

A chest x-ray should be obtained in patients with hypoxia and/or increased work of breathing, to evaluate for secondary infection or acute respiratory distress syndrome (ARDS).

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:

• Oseltamivir (Tamiflu®) – prevention and treatment in people 14 days and older; administered orally
• Zanamivir (Relenza®) – prevention and treatment; administered using an inhaler device
• Peramivir (Rapivab®) – treatment only in people 2 years and older; administered intravenously if oral medications are not tolerated

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.

Preventing Influenza

The best way to prevent influenza is through annual vaccination of everyone six months or older, and especially for those at increased risk for complications. Because influenza viruses evolve rapidly, flu vaccines are updated regularly to match which viral strains are expected to circulate. While the flu vaccine is not 100% effective, it can lower the severity and duration of symptoms in most people.

Some antiviral agents are indicated for prevention as well, but they should not be used as a substitute for annual vaccination. They may be indicated for patients for whom vaccination is contraindicated, such as anyone who has had a severe reaction to an influenza vaccination.

In addition, core methods for preventing disease include:

• Proper respiratory hygiene and cough etiquette
• Adherence to infection control precautions in the healthcare setting
  • Droplet precautions for seven days after illness onset or until 24 hours after the resolution of fever and respiratory symptoms
• Patient education, especially:
  • Avoiding contact with sick people
  • Covering one’s nose and mouth when coughing or sneezing
  • Washing hands with soap and water
  • Avoiding touching one’s eyes, nose, and mouth
  • Cleaning and disinfecting surfaces and objects that may be contaminated
  • Staying home for at least 24 hours after a fever is gone without medication (unless necessary to get medical care)
  • Practicing healthy habits such as getting adequate sleep, staying active, drinking plenty of fluids, and eating a healthy balanced diet