Influenza activity in Europe is very low, according to the first weekly electronic bulletin of the 2001-02 influenza season from the European Influenza Surveillance Scheme (EISS) (1).
Eight networks reported clinical influenza activity to EISS in week 42/2001 (15-21 October 2001). Seven networks reported no influenza activity (Belgium, Denmark, England, Germany, Ireland, Italy, and Switzerland), and a local outbreak of influenza was reported in Wales. The intensity of activity in all networks was low.
There are indications that influenza A and B viruses are circulating in Europe. The surveillance network in the Czech Republic reported two cases of influenza A in week 40/2001 and one case of influenza B in week 41/2001 (all reported by sentinel physicians). The GROG (http://www.grog.org/EuroGROG1.htm) surveillance network in France reported a case of influenza B (confirmed by immunofluorescence) in week 40/2001, in a baby admitted to hospital, and four cases of influenza were detected by sentinel physicians in week 42/2001 using a rapid influenza surveillance test (three cases in the Ile de France (Paris region), two aged 18 and one aged 51, and one case in Port-de-Bouc (near Marseille) aged 23).
The map presents the geographical spread of influenza as assessed by each of the networks in EISS. A=dominant virus A; H1=dominant virus A(H1N1); H3=dominant virus A(H3N2); B=dominant virus B.
The levels of influenza activity in European countries reported by EISS members during the 2001-02 influenza season are based on two assessments of influenza activity:
Each of these assessments is described below.
1. Indicators of the geographical spread of influenza:
Each network defines the geographical spread of influenza according to the definitions outlined below. The definitions are based on those used by the WHO global influenza surveillance system – FluNet (http://oms.b3e.jussieu.fr/flunet/).
ILI: influenza-like illness
ARI: acute respiratory infection
Country: Countries may be made up of one (for example, the Netherlands) or more regions (for example, France North and France South).
Region: The population under surveillance in a defined geographical sub-division of a country (for example, France North and France South). A region should not (generally) have a population of less than five million unless the country is large with geographically distinct regions.
No report: No report received.
No activity: Reports indicate no evidence of influenza virus activity. Cases of ILI/ARI may be reported in the country but the overall level of clinical activity remains at baseline levels and influenza virus infections are not being laboratory confirmed. Cases occurring in people recently returned from other countries are excluded.
Sporadic: Isolated cases of laboratory confirmed influenza infection in a region, or an outbreak in a single institution (such as a school, nursing home or other institutional setting), with clinical activity remaining at or below baseline levels. Cases occurring in people recently returned from other countries are excluded.
Local outbreak: Increased ILI/ARI activity in local areas (such as a city, county or district) within a region, or outbreaks in two or more institutions within a region, with laboratory confirmed cases of influenza infection. Levels of activity in the remainder of the region, and other regions of the country, remain at or below baseline levels.
Regional activity*: ILI/ARI activity above baseline levels in one or more regions with a population comprising less than 50% of the country’s total population, with laboratory confirmed influenza infections in the affected region(s). Levels of activity in other regions of the country remain at or below baseline levels.
* This term is not (generally) to be used in countries with a population of less than five million unless the country is large with geographically distinct regions.
Widespread activity: ILI/ARI activity above baseline levels in one or more regions with a population comprising 50% or more of the country’s population, with laboratory confirmed influenza infections.
2. Indicators of the intensity of influenza activity:
The intensity of influenza activity is based on the overall level of influenza activity in the country. Each network assesses the intensity of activity based on the historical data at its disposal. Some networks have historical data that date back over 30 years (for example, England and the Netherlands) and others have data that date back over shorter periods (for example, Belgium).
Some networks can establish numeric thresholds that define the intensity of influenza activity. For example, if the level of influenza activity rises above 200 cases per 100 000 population in England (and is below 400 cases per 100 000 population), the intensity of activity is considered to be “high” (“higher than average season activity”).
EISS uses the following definitions to indicate the intensity of influenza activity in each country:
Low: No influenza activity or influenza activity is at baseline level.
Medium: Level of influenza activity usually seen when influenza virus is circulating in the country based on historical data.
High: Higher than usual influenza activity compared with historical data.
Very high: Influenza activity is particularly severe compared with historical data.