Influenza activity in Europe during eight seasons (1999–2007): an evaluation of the indicators used to measure activity and an assessment of the timing, length and course of peak activity (spread) across Europe

Table 1 Comparison between clinical and virological peak incidences of ILI and ARI during eight influenza seasons in Europe (1999–2007)

	S. clinical vs. S. virological	S. clinical vs. S. virological	S. clinical vs. NS. virological	S. clinical vs. NS. virological
	ILI	ARI	ILI	ARI
1 week overlap	72%	71%	63%	46%
2 weeks overlap	84%	85%	84%	68%

S: Sentinel, information provided by sentinel general practitioners
NS: Non-sentinel, data obtained from non-sentinel physicians, hospitals and institutions
ILI: influenza-like illness used as case definition by 13 countries
ARI: acute respiratory disease used as case definition by 4 countries
1 week overlap: occurrence of peak incidences differ 1 week or less (good match)
2 week overlap: occurrence of peak incidences differ 2 weeks or less (moderate match)
Percentages represent the mean overall match aggregated from data of most participating countries obtained during 8 influenza seasons

ISSN: 1471-2334