Year	Cases per 100,000
1990	0
1991	0.1
1992	0.1
1993	0.1
1994	0.1
1995	0.2
1996	1.1
1997	2.8
1998	4.7
1999	5.9
2000	7.6
2001	9.5
2002	11.5
2003	13.6
2004	15.6
2005	18.6
2006	19.5
2007	20.5