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 in pregnancy, people aged over 65 years and in people with underlying chronic disease.

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)
  • 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 1 to 4 days (average 2 days).

Infectious period

People infected with influenza are considered infectious from 1 day before onset of symptoms up to 7 days from onset of symptoms. Viral shedding is greatest in the first 3 to 5 days of illness. Young children may shed virus for longer, up to 7 to 10 days. Viral shedding may continue for longer in severely immunocompromised persons.


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.


  • Encourage annual influenza vaccination. 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.
  • 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).


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.

Patients with uncomplicated influenza do not require antibiotics.

Managing influenza disease in pregnancy

The Managing pregnant women with suspected influenza fact sheet (PDF 75KB) 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.


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 to (08) 7425 6696.

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


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.