Table 2. Performance of the detection algorithm displayed with alert thresholds updated by using data from previous winter influenza seasons in evaluation of nowcasting for detection and prediction of local influenza epidemics, Sweden, 2009–2014*.

Influenza virus activity	Updated threshold, cases/d/100,000 population	Timeliness†	Interpretation
2009 pH1N1‡	0.424	−5	Good
2010–11 B and pH1N1	0.212	−5	Good
2011–12 A(H3N2)	0.207	15	Poor
2012–13 A(H3N2), B, and pH1N1	0.242	3	Excellent
2013–14 A(H3N2), B, and pH1N1‡	0.481	−3	Excellent

*pH1N1, pandemic influenza A(H1N1)pdm09 virus.
†Positive value means that the algorithm issued an alarm before the local epidemic had started; negative value means that the alarm was raised after the start of the epidemic.
‡The threshold was doubled because of a pandemic alert or observation of a period of simmering influenza activity.