| Year | Number of patients | Seronegative | Seropositive | % seropositivity |
| 1993 | 20 | 19 | 1 | 5% |
| 1994 | 20 | 18 | 2 | 10% |
| 1995 | 18 | 15 | 3 | 16.7% |
| 1996 | 28 | 25 | 3 | 10.7% |
| 1997 | 18 | 14 | 4 | 22.2% |
| 1998 | 34 | 18 | 16 | 47.1% |
| 1999 | 22 | 16 | 8 | 36.4% |
| 2000 | 30 | 16 | 14 | 46.7% |
| 2001 | 24 | 4 | 20 | 83.3% |
| 2002 | 40 | 15 | 25 | 62.5% |
| 2003 | 44 | 17 | 27 | 61.4% |
| 2004 | 58 | 23 | 35 | 60.3% |
| 2005 | 54 | 15 | 39 | 72.2% |
| 2006 | 74 | 18 | 56 | 75.6% |
| 2007 | 72 | 19 | 53 | 73.6% |
| 2008 | 76 | 10 | 66 | 86.8% |
| 2009 | 79 | 19 | 60 | 75.9% |
| 2010 | 101 | 24 | 77 | 76.2% |
| 2011 | 92 | 18 | 74 | 80.4% |
| 2012 | 103 | 22 | 81 | 78.6% |