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Analytical techniques - ISO 11731-2, SWAB and PVT
- ISO 11731-2 technique:
• With the traditional method of ISO, the recommendation is to collect
about 1 liter of sample of water, in this case, areas of difficult access render
unviable the collection. The sample collected in the field is then taken for
analysis in laboratory. However, the sample is not processed immediately.
According to the standard, the maximum limit between the collection and
the beginning of the test is up to 48 hours, which added to the processing
time, incubation and elaboration of the technical report, can take more
than 20 days to release the results. In case of outbreaks, it takes too long to
take an action.
• Transportation: The sample can suffer variations, such as interference
of total bacteria present in the water, i.e., during the transportation it can
occur excessive proliferation of these bacteria, thus impairing the search
for
Legionella
, besides, the effects of storage time on the exactness are
potentially much more severe for the tests of
Legionella
than for other
bacteria found in the water, which is related to the life cycle of
Legionella
,
which is predisposed to have host protozoa as parasites, mainly amoebae,
in such a way that at any time these protozoan can suffer lyse and release
thousands of viable
Legionella
in a relatively small volume of a sample
of water from a sole host cell. This condition would not be similar to the
hugely diluted concentration of
Legionella
from its place of origin, causing
an “erroneous” and alarming result that would take to drastic measures and
elevated costs.
• The delay between the collection and the start of the test can produce
a reversal of the previous situation, that is, due to the shortage of nutrients
