Lessons from a one-year hospital-based surveillance of acute respiratory infections in Berlin- comparing case definitions to monitor influenza

Table 2 Absolute and relative number of patients tested positive for pH1N1 by case definition and study period, hospital-based surveillance of acute respiratory infections, Berlin, 2009/10

		No. tested for influenza (%)	No. testing positive for influenza* (%)
CD1	Period 1	60/110 (55%)	16 (29%)
	Period 2	294/915 (32%)	4 (1%)
	Total	354/1,025 (35%)	20 (6%)
CD1b	Period 1	32/71 (45%)	7 (25%)
	Period 2	174/671 (26%)	2 (1%)
	Total	206/742 (28%)	9 (5%)
CD4	Period 1	28/39 (72%)	9 (32%)
	Period 2	120/244 (49%)	2 (2%)
	Total	148/283 (52%)	11 (8%)

ISSN: 1471-2458