Year	Cases per 100,000
1990	0.1
1991	0.2
1992	0.3
1993	0.5
1994	0.7
1995	0.9
1996	1
1997	1.2
1998	1.3
1999	1.5
2000	1.6
2001	1.7
2002	1.8
2003	1.8
2004	1.8
2005	1.7
2006	1.5
2007	1.4