| Year | Number of people affected |
| 1975 | 16,000 |
| 1977 | 20,000 |
| 1980 | 40,000 |
| 1984 | 200,000 |
| 1992 | 1,500,000,000 |
| 1995 - 1996 | 1,400,000,000 |
| 1999 - 2000 | 4, 400,000,000 |
| 2004 - 2006 | 3,500,000,000 |