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

From: 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

  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%
  1. S: Sentinel, information provided by sentinel general practitioners
  2. NS: Non-sentinel, data obtained from non-sentinel physicians, hospitals and institutions
  3. ILI: influenza-like illness used as case definition by 13 countries
  4. ARI: acute respiratory disease used as case definition by 4 countries
  5. 1 week overlap: occurrence of peak incidences differ 1 week or less (good match)
  6. 2 week overlap: occurrence of peak incidences differ 2 weeks or less (moderate match)
  7. Percentages represent the mean overall match aggregated from data of most participating countries obtained during 8 influenza seasons