The objectives of this study were to describe time trends in the
detection of two commonly applied indicator organisms of faecal
contamination in commercially cultured blue mussels (M. edulis)
harvested along the coast of Norway during the six-year period
from 2007 to 2012. Possible covariance in the occurrence and
concentration of E. coli and enterococci, and the effect of precipitation
(rainfall or snow) in the period of examination, were
assessed. Several localities for bivalve cultivation in Norway
showed single high counts of E. coli, without a previous history of
E. coli detection. One other pattern of E. coli detection was repeated
low values above the limit and some higher values in between.
There also seemed to be a weak positive correlation between
detection of enterococci and E. coli, and aweak correlation between
the number of E. coli/enterococci and rainfall. Due to the low
numbers of enterococci present in the current sampling material,
the detections and quantifications of enterococci in this study were
uncertain. Hence, if enterococci are to be used as indicator organisms
of faecal contamination in bivalves, an MPN method with
lower dilutions should be considered.