| Risk occurrence possibility score | 1 | 2 | 3 | 4 | 5 |
| Risk occurrence possibility | Very low frequency | Relatively low frequency | General frequency | Relatively high frequency | Very high frequency |
| Description of risk occurrence possibility | An average of less than one cases per year | An average of one or more cases per year, but less than 4 cases per year | An average of one or more cases per season, but less than 3 cases per season | An average of one or more cases per month, but less than 4 cases per month | An average of one or more cases per week |