Influenza surveillance country profiles of WHO European Region Member States
The characteristics of the influenza surveillance systems presented in the country profiles include:
- type of surveillance system;
- number and type of health facilities participating and the population covered by these facilities;
- case definition used;
- year of introduction of the surveillance system;
- use of an epidemic threshold;
- reporting frequency; and
- laboratory methods used for influenza testing.
Finally, a map presents the locations of participating health facilities or hospitals if available.
Primary care and hospital surveillance
A distinction has been made between surveillance in primary (outpatient) care for mild disease and in hospitals for severe disease. For primary (outpatient) care surveillance, two types of surveillance are frequently performed: influenza-like illness (ILI) and acute respiratory infection (ARI). At the inpatient level a surveillance system for hospitalized severe acute respiratory infection (SARI) is mainly used, but hospital surveillance among laboratory-confirmed influenza cases can be carried out as well. Only those surveillance systems from which data are reported weekly to Flu News Europe are presented.
Types of surveillance systems
In general, there are two types of surveillance systems: sentinel and non-sentinel. Sentinel surveillance involves a limited number of selected healthcare providers or hospitals that report specified health events that may be generalizable to and representative for the whole population. Non-sentinel surveillance is the term used when samples are collected from other sources e.g. practices and/or hospitals not participating in the sentinel surveillance system. In universal surveillance systems, all healthcare providers or hospitals report the occurrence of specified health events.