Year Cases per 100,000 1990 0 1991 0 1992 0 1993 0 1994 0 1995 0 1996 0 1997 0 1998 0 1999 0.1 2000 0.1 2001 0.2 2002 0.4 2003 0.7 2004 1.1 2005 1.7 2006 2.2 2007 2.6