Table 1.

Definitions and comparison of intensity levels with EISN and MEM criteria

EISN (European Influenza Surveillance Network)		MEM (moving epidemic method)
Intensity level	Definition	Intensity level	Definition
1. Low	No influenza activity or influenza activity is at baseline level*	1. Baseline/pre-epidemic	ILI rate below the epidemic threshold†
2. Medium	Level of influenza activity usually seen when influenza virus is circulating in the country based on historical data	2. Low	ILI rate between epidemic and medium threshold‡
		3. Medium	ILI rate between medium and high thresholds§
3. High	Higher than usual influenza activity compared to historical data	4. High	ILI rate between high and very high thresholds||
4. Very high	Influenza activity is exceptionally high compared to historical data	5. Very high	ILI rate above very high threshold

ILI, Influenza-like illness; CI, confidence interval.

^*Baseline influenza activity is the level that clinical influenza activity remains throughout the summer and most of winter.

^†95% CI of the arithmetic mean of the 30 highest pre-epidemic weekly ILI rates within the last ten (or the available number) influenza seasons.

^‡40% CI of the geometric mean of the 30 highest epidemic weekly ILI rates from the same historical period of time.

^§90% CI of the geometric mean of the 30 highest epidemic weekly ILI rates from the same historical period of time.

^||97·5% CI of the geometric mean of the 30 highest epidemic weekly ILI rates from the same historical period of time.

Note that medium intensity level according to the criteria of EISN includes the low and medium intensity levels calculated with MEM criteria.