Table 1.

Characteristics of data sets by country

Region	Seasons	Numerator	System	Nature	Denominator	Units	Average
Influenza‐like illness data
Belgium	10	ILI	Sentinel	Voluntary	Population*	×100 000	–
Castilla y Leon (Spain)	14	ILI	Sentinel	Voluntary	Population	×100 000	40 000
Greece	6	ILI	Sentinel	Voluntary	Consultations	×10 000	6000–20 000**
Hungary	7	ILI	Sentinel	Compulsory	Population	×100 000	2000 000
Ireland	10	ILI	Sentinel	Voluntary	Population	×100 000	263 235
Israel	12	ILI	Sentinel	Voluntary	Population	×100 000	1 900 000
Kyrgyzstan	5	ILI	Nationwide	Compulsory	Population	×100 000	5 383 27
Norway	6	ILI	Sentinel	Compulsory	Population	×100 000	600 000–700 000
Poland	9	ILI	Sentinel	Voluntary	Population	×100 000	1 50 000
Portugal	12	ILI	Sentinel	Voluntary	Population	×100 000	56 000
Romania	5	ILI	Sentinel	Compulsory	Population	×100 000	600 000
Slovenia	10	ILI	Sentinel	Voluntary	Population	×100 000	75 000
Spain	14	ILI	Sentinel	Voluntary	Population	×100 000	813 371
Switzerland	9	ILI	Sentinel	Voluntary	Population*	×100 000	–
The Netherlands	15	ILI	Sentinel	Voluntary	Population	×100 000	116 000
Acute respiratory infection data
Albania	7	ARI	Nationwide	Compulsory	Population	×100 000	3 161 337
Kazakhstan	5	ARI	Sentinel/Nationwide	Compulsory	Population	×100 000	16 776 539
Romania	5	ARI	Sentinel	Compulsory	Population	×100 000	600 000
Russian Federation	6	ARI	Nationwide	Compulsory	Population	×100 000	44 267 62
Ukraine	7	ARI	Clustering***	Compulsory	Population	×100 000	98 892 550

^*Population is estimated from the number of consultations per week. GPs have not a fixed patient list.

^**Average number of consultations per week.

^***Compulsory system within a sample of cities of the country.