Table 3. Age stratified number of sera tested and percentage of sera with reactivity to any norovirus antigen.

	1963		1983		2006/2007
Age group(years)	n sera tested	Sera norovirus positive (%)	n sera tested	Sera norovirus positive (%)	n sera tested	Sera norovirus positive (%)
<1	25	72.0	20	70.0	110	42.7
1 to <2	32	50.0	23	56.5	57	64.9
2 to <3	25	72.0	34	67.6	74	63.5
3 to <4	27	66.7	24	79.2	75	85.3
4 to <5	34	85.3	29	75.9	60	85.0
Total	143	69.2	130	70.0	376	65.4