Risikovurdering og risikoprofil af forekomst af coliforme bakterier i ...

“Worst case” is an extreme scenario, and the coliform values should be considered
extreme. However, the calculations did not include any safety factors (normally a
safety factor of 1 out of 10,000 is considered) so “worst case” will be the safest
background for evaluation.
For sewage were there sufficient data to consider coliform and E. coli data
separately. In the “worst case” scenario coliforms will always identify the health
risk for 5 pathogens, while E. coli always will identify the health risk from 4
pathogens. Since the E. coli concentration in the source is lower or equal to the
coliform concentration, the risk of not identifying a contamination causing a health
risk will increase if only E. coli is used as indicator organism.
The scenarios and the outbreak data from the literature showed, that in several
cases – epically for virus - a negative coliform analysis is not a guarantee against a
health risk. Only in few cases, the results could be considered a false positives i.e.
identification of coliforms without the infectious dose of a pathogen being ingested
via the daily 2 L of drinking water. Based on the reports evaluation of health risks
in the “worst case” scenarios, there is no justification for raising the parameter
value for coliforms due to the current value causing false positive samples. This
conclusion should, however, be seen in the light of the relative small data basis.
Since the water supply in Denmark is based on ground water, which can be
considered free of coliforms, the presents of coliforms will always indicate an
intrusion from outside, thus identification of coliforms should always lead to
further investigations.