Year Cases per 100,000 1990 0 1991 0 1992 0 1993 0 1994 0 1995 0.1 1996 0.2 1997 0.2 1998 0.4 1999 0.6 2000 0.9 2001 1.4 2002 2.2 2003 3 2004 4.2 2005 5.6 2006 7.3 2007 9.1