Influenza Surveillance Reports

In the Northern Hemisphere, influenza season commences in October and continues through to May. In general influenza outbreaks last between 6 - 8 weeks and can affect all ages, in particular the extremes of age. Influenza surveillance can provide information that may help in the management of such an outbreak.

Influenza surveillance involves collection of both clinical and virological data. Clinical surveillance monitors the impact of the illness on the health service and the community, while virological surveillance confirms that influenza is circulating and also identifies the current strain.

The Health Protection Surveillance Centre in partnership with the Irish College of General Practitioners (ICGP) and the National Virus Reference Laboratory (NVRL) have established a network of 60 computerised general sentinel practices who report on a weekly basis the number of patients seen with influenza-like illness. Influenza-like illness is characterised by the sudden onset of symptoms with a temperature of 38°C or more, in the absence of any other disease, with at least two of the following: dry cough, headache, sore muscles and a sore throat.

As there is little difference in the presenting symptoms of a number of respiratory pathogens, virological confirmation is required to identify that influenza is the causative agent. The NVRL can detect and identify if influenza A and/or B viruses are circulating. Further identification of subtypes of influenza A isolates is also carried out. Samples received at the NVRL undergo polymerase chain reaction studies, cell culture and virus isolation.

Following collection of the data, an Influenza, RSV and Other Respiratory Viruses Surveillance Report is compiled. The report will be produced every Thursday throughout the influenza season, which runs from October to May. The frequency of the report will reduce to fortnightly towards the end of the season in April and May. Both graphs and tables will be used to display the clinical and virological data from the sentinel practices and the NVRL. The report is provisional until all data has been collated and may alter from week to week as it is updated. 

Reports of influenza activity in Europe and worldwide will also be provided as part of the overall monitoring of influenza activity.