Biology Reference
In-Depth Information
Investigative monitoring covers a range of scenarios. For example, at pres-
ent, the assessment of source water quality relies upon estimates of the num-
bers of waterborne pathogens present, either by extrapolation from literature
data or applying models to predict the transport of pathogens into the water
source from surrounding land. Both methods involve many assumptions and
therefore lead to uncertainty in the risk assessment. Investigative monitoring
to accurately identify the numbers and types of pathogen in particular sources
of drinking water would enable water providers to properly assess risks and
reliably estimate the disease burden associated with a particular water supply.
This type of testing will require pathogen speciation, or even more detailed
investigation. For example, many waterborne pathogens, such as all Vibrio
species, have to be identified beyond the species level to determine their
pathogenic potential. 5,6 This can also be known as microbial source tracking
(MST) or fecal source tracking. 7,8 When MST is applied to identification of
the source of an outbreak, rapid monitoring methods are also required.
3.3. FECAL INDICATOR MONITORING
During the twentieth century, the measurement indicator of bacteria in
finished water has contributed to a significant improvement in drinking water
safety. This strategy assumes that fecal indicators, showing that waters have
been fecally contaminated, will therefore, also, indicate the presence of any
pathogens. Commonly used, indicator bacteria studies include thermotolerant
coliforms, fecal coliforms and, more recently, Escherichia coli . 9 The advantages
of this approach are that these tests are relatively cheap and easy to perform.
However, there are concerns about the degree of correlation between the
detection of indicators and presence of microbial pathogens, as well as the fact
that this approach does not allow a valid identification of the pathogen. 10
Indicator monitoring takes time for the growth by culturing and, there-
fore, it is retrospective; some contaminated drinking water may have already
been consumed before a problem has been detected. This has led to the view
that this type of monitoring is more compatible with a quality assurance
scheme, whereby the absence of an indicator provides reassurance that the
hygienic quality of the water supply system has not yet been compromised.
Routine monitoring of drinking and recreational waters for bacterial
pathogens is based on detecting indicator organisms to assess water quality. 11
The bacteria that probably satisfies this criteria best is E. coli . It is a member
of the coliform group of bacteria. The coliform group comprises all of the
 
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