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Clinical management information

Incubation period

While the maximum incubation period could be seven days, a shorter median incubation period of three days seems typical.

Infectious period

The infectious period is assumed to be from 24 hours (one day) prior to the onset of symptoms until either seven days after the onset of symptoms or until the resolution of fever – whichever is longer.

It is possible that some groups, especially children, might be contagious for longer periods, but for practical purposes of public health control it is recommended that the infectious period should be considered to be the same for all groups.

However, for defining the isolation period, a case can be assumed to be no longer infectious 72 hours after anti-influenza medication is commenced, provided fever has resolved.

Note: this may change as more information becomes available about the disease.

Mode of transmission

Airborne spread through large droplet nuclei is believed to be the primary mode of transmission, through coughing and sneezing by infected persons. Contact transmission (direct and indirect) is also thought to be an important mode of transmission. Human influenza viruses may persist for hours on solid surfaces, particularly in lower temperatures and lower humidity.

GP Summary: 18 June 2009

For general summary on pandemic (H1N1), including vulnerability, testing, antivirals, state and territory contact see H1N1 Influenza 09 (PROTECT PHASE) Summary Sheet for General Practitioners (PDF 88 KB).

Clinical management of patients with presumptive or confirmed infection: July 2009

Guidance for clinicians on patient management is available in the Clinical Management of pandemic (H1N1) 2009 resource (PDF 173 KB). This should be read in conjunction with current advice on the diagnosis of this infection, as well as resources available concerning the current pandemic phase and the focus of investigation, treatment and public health measures at the time.

GP Clinical Update: August 2009

The GP Clinical Update (PDF 30 KB) provides information on accumulating evidence on the clinical presentation of pandemic H1N1 2009; the sensitivity of laboratory testing for pandemic H1N1 2009, and signs and symptoms associated with rapidly deteriorating disease.

Case management

Individuals with mild disease who are not in a vulnerable group should only require symptomatic management. They should be isolated at home for the appropriate period, but do not require antiviral medication.

Clinical assessment with early and intensive management (including antiviral medication) of vulnerable cases with influenza is important.

Figure 1: Decision tree for management of cases of Acute Respiratory Illness (ARI)

Moderate or severe disease, or those who are rapidly deteriorating

Cases with moderate or severe disease, or those who are rapidly deteriorating should also be considered for antiviral medication. Antiviral medication should be started as soon as possible, and preferably within 48 hours of onset of symptoms.

Signs of moderate to severe disease or deterioration would include:

1. Respiratory distress – noticeable respiratory effort, rapid breathing or noisy breathing in a person at rest.
2. Abnormal oximetry – measurement of a low haemoglobin-oxygen saturation (SpO²) using pulse oximetry
3. Purulent sputum – in normal people the development of green or yellow sputum correlates reasonably well with bacterial bronchitis or pneumonia.
4. Reduced exercise capacity – some people, both normals and those with chronic medical conditions, have a very good appreciation of their usual exercise capacity. If this is significantly reduced because of worsening breathlessness during an episode of influenza, the possibility of respiratory complications should be considered, although this is a non-specific symptom
5. “Loss of function” – in the elderly severe influenza, including pneumonia, frequently (most commonly) present as loss of function such as confusion, falls and incontinence.
   • The pandemic (H1N1) 2009 virus is susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza), but is resistant to amantadine.
   • Identified cases should be isolated at home until the diagnosis is excluded or the infectious period is over. This will be 7 days from illness onset if no antiviral medication is taken, or 3 days from the onset of antiviral medication therapy. In either case, the period may be extended if there is ongoing fever at the end of these periods.
   • Cases in home isolation should wear a surgical mask when in the same room as other household members and stay at least 1 metre distant. Where possible they should sleep in a separate room.
   • Case isolation may be ceased when the case is no longer in the infectious period, or when H1N1 09 has been excluded OR an alternative diagnosis that is consistent with the case’s symptoms has been made.

See also: Clinical Management of pandemic (H1N1) 2009 resource (PDF 173 KB)

If you are having difficulty downloading the PDF document(s) please email webmaster@health.gov.au and we will arrange for an alternative format or a copy to be sent to you.