Influenza information for health professionals

Influenza commonly known as the flu is a highly contagious infection of the nose, throat and lungs caused by the influenza A or B (or rarely C) viruses.

Influenza is a notifiable condition

Clinical presentation

In South Australia, influenza is most common in the winter months.

Influenza causes a spectrum of illness from asymptomatic infection to fatal pneumonia (primary viral or secondary bacterial). Severe disease is more common for the following groups:

  • pregnant women
  • people aged over 65 years
  • people with underlying chronic disease
  • children aged 6 months to less than 5 years
  • Aboriginal and Torres Strait Islander people
  • residents of aged care or long-term residential facilities
  • people experiencing homelessness.

Doctors should consider influenza in anyone with:

  • fever greater than 38oC or a good history of fever (note: fever may be absent in older people)
    AND
  • cough or sore throat, in the absence of any other explanation for symptoms.

Most people with uncomplicated influenza recover within a week, although the cough and fatigue may last longer.

Mode of transmission

Spread is via respiratory droplets and direct contact with respiratory secretions.

Incubation period

Incubation period is one to four days (average two days).

Infectious period

People infected with influenza are considered infectious from one day before onset of symptoms up to seven days from onset of symptoms. Viral shedding is greatest in the first three to five days of illness. After five days, the level of infectiousness is probably very low. Young children may shed virus for longer, up to seven to ten days. Viral shedding may continue for longer in severely immunocompromised persons.

Diagnosis

Laboratory testing is not always necessary in the case of mild illness.

Take a deep nasal or throat swab, or sputum for respiratory viral testing. Use appropriate personal protective equipment when obtaining the sample.

Prevention

  • Encourage annual influenza vaccination from April onwards for protection during the peak season, This is typically May to September in most parts of Australia. Vaccination against influenza has the primary aim of reducing severe influenza. Annual flu vaccination is strongly recommended for anyone 6 months of age and older and should be actively promoted for people at increased risk of complications.  Due to changes in circulating strains and waning immunity, vaccination is required each year.
  • The National Immunisation Program (NIP) provides free influenza vaccines to people at increased risk of complications from influenza.
  • Encourage respiratory etiquette and hand hygiene:
    • cover a cough or sneeze with a tissue or arm (not hands)
    • drop used tissues immediately into a rubbish bin
    • wash hands with soap and running water, or use an alcohol-based hand rub, after sneezing, coughing or touching used tissues.
  • In healthcare settings, institute contact and droplet precautions. 
  • Consider prescribing antivirals. Antivirals can be given after known exposure to influenza. Prophylactic antivirals are usually only used in persons at high risk of severe influenza. If used, prophylaxis should be commenced within 48 hours of exposure.
  • Exclude cases from childcare, preschool, school or work until there has been no fever for 24 hours (without using an antipyretic).

Treatment

Medically assess the need for hospital presentation/admission.

Consider antivirals for treatment in:

  • patients with established complications or severe illness (for instance, needing hospitalisation)
  • patients from high-risk groups
  • patients not in high-risk groups and not severely unwell if commenced within 48 hours of onset.

Managing influenza disease in pregnancy

The Managing pregnant women with suspected influenza fact sheet (PDF 100KB) provides health professionals with information on influenza prevention, testing, treatment and prophylaxis in pregnant women.  Important considerations in influenza management during each trimester, delivery and in the post-partum period are also discussed.

Notification

Medical practitioners are required to notify seasonal influenza to the Communicable Disease Control Branch, South Australia ONLY where (a) they suspect a person has died from the condition or (b) they have conducted a point of care test that has returned a positive result which is not also reported by a pathology service. If one or both of these scenarios apply, notify online or download and fax the purple notification form (PDF 1028KB) to (08) 7425 6696.

Note: there is a still a requirement for medical practitioners to notify avian influenza in humans. Telephone: 1300 232 272.

Surveillance

The Communicable Disease Control Branch conducts statewide surveillance of all notifiable conditions (including influenza) in South Australia. This includes a chart that provides a regular update on influenza activity in South Australia.

Nationally, the Australian Influenza Surveillance Report and Activity Updates provides national data monitoring influenza activity and severity.