Last updated:
17 July 2006
1. Reason for surveillance
- To monitor trends in influenza incidence
- Where outbreaks in residential care facilities are reported, to advise on control.
2. Case definition
A confirmed case requires laboratory definitive evidence only. Laboratory definitive evidence
- Isolation of influenza virus by culture from an appropriate respiratory tract specimen, or
- Detection of influenza virus by nucleic acid test from an appropriate respiratory tract specimen, or
- Detection of influenza virus antigen from an appropriate respiratory tract specimen, or
- IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to influenza virus, or
- Single high titre to influenza virus by complement fixation or haemagglutination inhibition.
Factors to be considered in case identification
Rapid point-of-care influenza test kits have a relatively high false negative rate, and so cannot exclude influenza diagnosis in an individual with influenza symptoms. However in an outbreak setting where samples from multiple patients are tested, they can be useful in identifying influenza as the causal agent in patients with the influenza symptoms.
3. Notification criteria and procedure
Influenza is to be notified by:
- Laboratories on diagnosis (by routine mail).
Confirmed cases only should be entered onto NDD.
4. The disease
Infectious agent
Influenza viruses are divided into three types A, B and C. Type A have been linked with widespread epidemics and pandemics. Regional or widespread epidemics have been linked to type B influenza, and type C has been linked with sporadic cases and minor localised outbreaks and is rarely reported. Mode of transmission
Influenza is spread from person-to-person by infectious droplets. Transmission may occur through direct and indirect (fomite) contact. The virus may persist on fomites for up to 2-3 days, particularly in cold or low humidity conditions. Timeline
The typical incubation period for seasonal influenza is 1-3 days. Adults are usually infectious for 3 to 5 days, and small children for up to 7 days, after onset of illness. Severely immunocompromised persons may shed virus for longer. Clinical manifestations
An infected person generally has a sudden onset of:
Compared with other viral respiratory infections, influenza causes more severe complications such as pneumonia, particularly in elderly people and other vulnerable groups.
5. Managing single notifications
Response time
Investigation
No public health investigation is required for sporadic cases of seasonal influenza. Where an outbreak in a residential facility is reported, see section 6. Other specific protocols address PHU responses to reports of avian influenza and pandemic influenza. Data entry
Within 3 working days of notification enter confirmed cases on NDD. Response procedure
Not applicable for sporadic cases of seasonal influenza. Case management
Not applicable for sporadic cases of seasonal influenza. Contact management
Not applicable for sporadic cases of seasonal influenza.
6. Managing special situations
Outbreak in a residential care facility (RCF)
Where three or more cases of newly acquired respiratory illness in staff and/or residents in a RCF within a period of seven days is reported, the PHU should provide advice to the Director of the facility according to the national Guidelines for the Prevention And Control of Influenza Outbreaks in Residential Care Facilities, September 2005.
Note that the Commonwealth's Influ-Info Influenza Kit for Aged Care also provides useful information for facilities,
Within one working day, contact CDonCall by email or telephone with the following information:
- Name and location of the facility
- Total number of residents and staff in the facility
- Date of onset of the first case
- Approximate number of cases to date
- How many samples have been collected and how many were positive for influenza
- Brief summary of outbreak control measures already initiated or planned.
Complete a report form and forward to the CDB (fax: 9391 9189 or by email: CDonCall@doh.health.nsw.gov.au together with an epidemic curve including at least preliminary data within 2 weeks of the end of the outbreak. Fax the form with the final data within 4 weeks of the end of the outbreak. Notes on the use of antivirals
RCFs should be encouraged to source antivirals through their usual pharmaceutical supply chain. The prescribing and administration of the oseltamivir is ideally managed by the GPs who attend the facility. Because anti-virals may be difficult to obtain, particularly at periods of widespread influenza activity, in 2006 NSW Health provided a one-off allocation of 100 courses of oseltamivir to each AHS PHUs for use in outbreaks.
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