Sample Processing - Waterborne Pathogens: Detection Methods and Applications - page 65

5. Applicable to a wide range of environmental water matrices, e.g. drink-
ing water and wastewater; and
6. A simple and inexpensive procedure that can be carried out in most
environmental or water quality laboratories ( Box 4.1 ).
Definitions of the Important Factors in Waterborne Pathogen
Sample Processing Techniques
Recovery rate —this refers to the efficiency of the process in capturing and concen-
trating all of the pathogens of interest; i.e. a highly successful process would have a
recovery rate of 100% indicating that all of the pathogens in the original sample are
in the concentrated sample. Recovery rates are in general significantly lower than
this and, in some cases, rates as low as 10%-20% are considered acceptable. Recov-
ery rate is particularly important for pathogens present in low numbers, as if the rate
is low any pathogen in the sample might be lost during the sample processing stage.
Degree of concentration —this indicates to what extent the sample has been
concentrated, for example a concentration factor of 10 2 means that the volume
of the original sample has been reduced 100 times. So if a 100 mL sample was
used, it would be concentrated to 1 mL.
Specificity of isolation —this term refers to how selective the method is for the
pathogen of interest and applies to techniques aiming to enrich the presence of
a certain pathogen from mixed samples, e.g. immunomagnetic separation (IMS)
which depends upon the cross-reactivity of the antibody to confer specificity;
antibody specificity can vary between different pathogens.
Water/sample matrix —this describes the type of water from which the sample
is taken, e.g. raw source water from rivers, lakes, reservoirs or groundwater; finished
drinking water; or wastewater. Evidently, these different water types will contain
different amounts of interferents (inorganic, organic, or microbial matter) and have
different physicochemical characteristics (temperature, pH, conductivity, etc.),
which could influence the performance of different sample processing techniques.
False positives —results indicating pathogen presence when, in fact, the sam-
ple is pathogen free.
False negatives —results indicating that the sample is pathogen free when, in
fact, it contains pathogens.
Precision —how close the measured value(s) or indicator is to the true value.
Conidence —the likelihood that this measured value is within the defined
precision.
The Water Framework Directive is based on a risk assessment exercise, where
precision and confidence are described, respectively, as how close the measured
value(s) or indicator is to the true value and the likelihood that this measured
value is within the defined precision. Adequate precision and confidence in val-
ues obtained through monitoring are essential to allow an acceptable level of
risk in the decision-making process. 14