Influenza viruses
Saturday 13th March 2010
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Influenza viruses
There are two parts to the influenza surveillance system in New Zealand, one is general practice (GP) sentinel surveillance and the other is laboratory-based surveillance.(top)
Sentinel Surveillance
The sentinel surveillance system commenced in 1991 as part of the WHO (World Health Organisation) global programme for influenza surveillance. It is operated nationally by ESR and locally by surveillance co-ordinators within the public health service in each health district. The system operates during the 'influenza season', from May through September each year.It is based on a network of voluntary sentinel GPs distributed on a population density basis of approximately 1 per 50,000. Sentinel General Practices carry out both disease and virological surveillance. Each sentinel practice records the daily number of consultations that fit a case definition for an influenza-like illness (ILI), along with the patient's age, on a standardised reporting sheet.
The influenza case definition is "an acute respiratory tract infection characterized by an abrupt onset of two of the following: fever, chills, headache and myalgia". This data is either collected by phone, or forwarded by fax each Friday. Consultation rates are calculated using the number of consultations as the numerator and the sum of the patient populations, reported by the participating practices, as the denominator.
The national level of ILI activity is described using a set of threshold values: a weekly rate of 50-249 consultations per 100,000 patient population is considered indicative of normal seasonal activity; 250-399 indicates higher than expected activity, and >= 400 indicates an epidemic level of disease.
Each sentinel practice also provides respiratory samples from the first patient seen with an ILI on Monday, Tuesday and Wednesday of each week, which are forwarded to four regional virus diagnostic laboratories at Auckland, Waikato, Christchurch and Dunedin hospital and ESR virology laboratory for virus isolation and identification.
Weekly consultation data, along with virus isolation data, are forwarded by local co-ordinators to ESR each Monday. Collated national data are presented in reports weekly, monthly and annually.
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Laboratory-based Surveillance
The year-round laboratory-based surveillance of influenza and other viruses, is carried out by the four regional laboratories and by the ESR virology laboratory. These laboratories report all virus diagnoses made, largely from hospital in-patients and outpatients, to ESR. These data are reported nationally in the ESR Virology Weekly Report.(top)
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Make sure you are alerted by email when selected new reports become available. Alerts are not available for the Weekly Influenza Update report, please check the website every Thursday for an update. More |
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