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 2000 0 2001 0.1 2002 0.3 2003 0.7 2004 1.4 2005 2.6 2006 3.6 2007 4.2