Extract from Sampling of Households for Legionella Species
(J V LEE & S B SURMAN (2002) Sampling of households for Legionella species
http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947390280 http pdf)
Method
Samplers should be aware that samples may need to be divided so as to provide duplicate
sub-samples for legal purposes. If this is the case, a minimum of 2 litre samples should be
collected.
4.1 Layout of hot and cold water system
On entering the property carry out a preliminary survey to establish the layout of the
hot and cold water system. Make a schematic diagram of the system that can be used later to
clearly indicate where samples were collected. Establish the position of the header tank (if
any) and water heater and all hot water outlets (taps, shower heads, etc.) on the system
supplied by the hot water heater. Note the materials used for the piping and outlets (copper,
galvanised steel, polybutylene, PVC etc). Determine which outlet is the nearest to the water
heater (has the shortest length of pipe joining it to the water heater) and which is the
furthest from the water heater (has the longest length of pipe joining it to the water heater).
In large systems determine if any particular outlets were used by the patient.
In blocks of flats the cold water may come from a communal cold water tank in which case this
should also be investigated. Occasionally communal hot water systems that serve many flats may
be encountered. These should be investigated and are akin to investigating systems in hotels or
hospitals.
4.2 Water heater
Inspect the water heater. Note the type of heater i.e. electrical immersion;
indirect from the central heating hot water; indirect with electrical immersion heater back-up
etc. Note the construction materials and insulation. Record the temperature setting on the
thermostat and for how long each day the heater is switched on. Follow the piping as much as
possible and note where the nearest tap to the water heater is situated and the location of the
furthest.
4.3 Hot outlet nearest to water heater
4.3.1 Immediate hot water sample
Record where the outlet is and its type (single tap, mixer tap, shower etc). If it is a
shower follow the procedure described in paragraph 4.5 below. If it is a combination mixer tap
with a shower outlet collect the following samples from the shower first using the sampling
method described in paragraph 4.5 below. Label a sample container indicating the site etc and
that this is the immediate sample. Record if the tap has any defects (dripping, leaking glands
etc.). Collect 1 litre of water and reseal the container. Run the tap for one minute and note
the temperature. Precautions should be taken to minimize aerosol or spray production.
4.3.2 Post flush hot water sample
This sample is taken to obtain a sample representative of the pipe work and hot water
cylinder rather than the colonisation of the outlet. It is preferable to collect such a sample
from a simple tap rather than a mixer tap. If the tap used to collect the sample above was not
a simple tap select an alternative if one is available. Clean the outside of the tap with an
alcohol wipe or hypochlorite solution and, if the tap has not already been sampled, run the tap
for about one minute. Disinfect the inside of the tap by squirting the disinfectant solution up
inside the orifice of the tap. Wait for two minutes, turn the tap on and allow it to run for a
further minute and then collect the sample without adjusting the flow of the water. Label it
"post flush sample" in addition to noting its source etc.
4.4 Hot water tap furthest from hot water cylinder
Also collect an immediate sample from the hot water tap furthest from the hot water cylinder.
This will normally be the kitchen tap.
4.5 Sampling showers
Inspect the shower noting its type (mixer connected to hot and cold tap on bath, separate
pumped shower, instantaneous electrically heated shower etc) if it has a flexible hose or not
and if it has any faults including dripping, scaling and mould growth or other deterioration of
the hose, and whether the cold water is supplied to the mains directly. If connected to the hot
water system set the temperature to maximum. For instantaneous showers leave the setting at its
lowest temperature setting with the heater on (i.e. not on the cold setting where the
electrical heater does not operate at all). Label a bottle and remove its cap storing it in a
clean new plastic bag. Cut the end or a comer off a new food grade plastic bag. Insert the
shower head into the plastic bag and hold the bag closed around the shower hose behind the
shower head. Insert the other end of the bag into the open sample container. Keeping the bag
closed behind the shower head (a rubber band may be used to facilitate this), carefully turn on
the water flow so that a gentle flow is created and the water flows into the container.
Alternatively remove the shower head, being careful not to lose any water that may be in the
shower head, and collect the sample from the shower hose. Collect one litre of water and note
the temperature after allowing it to flow for one minute as before.
4.6 Header tank
4.6.1 In order not to disturb sludge or biofilm prior to taking the samples as described
above, the header tank should be inspected and sampled last.
4.6.2 Inspect the header tank for the domestic hot water system. Be careful you do
not confuse it with the central heating header tank. If you are not sure, leave a hot water tap
running. The ball valve in the tank feeding the hot water system will eventually operate to let
in fresh water. Note how well the tank is insulated, whether it is covered, the materials of
construction, and the volume of water stored. Remove or push aside the cover so that the end
furthest away from the inlet is uncovered. Take care not to allow dirt to enter the tank.
Inspect the inside, noting if it is corroded, dirty etc.
4.6.3 Collect a sample of water from the tank using a sterile dip sampler or syphoning
device or simply by dipping the sample bottle into the water. In the latter case particular
care should be taken to avoid a cross contamination of samples. Wear a new pair of disposable
gloves, disinfect the outside of the bottle with an alcohol wipe and allow the alcohol to
evaporate away before collecting the sample. Seal the bottle. Dry the outside of the bottle
with a fresh towel and discard the towel. Wipe the outside of the bottle with an alcohol wipe.
Note the temperature of the water in the tank. Disinfect the thermometer after each use with an
alcohol wipe. Change gloves before collecting the next sample.
4.6.4 Recover the tank making sure not to allow dirt to enter it.
4.7 Cold water
4.7.1 Bathroom cold tap
Collect an immediate sample of cold water from a bathroom cold tap noting if it is
supplied from the cold water header tank or directly from the main. An indication of this can
be obtained from the water pressure, which should be high if it is off the main. Measure the
water temperature after the water has flowed for two minutes.
4.7.2 Incoming mains water
The kitchen tap should be connected to the main water supply. Use this to collect a
sample representative of the incoming water. Run the tap for a minute and clean and disinfect
it as in paragraph 4.4.2 above and collect a post flush sample.
4.7.3 Water closets
Water closet cisterns can become heavily colonised in areas with high ambient
temperatures and should not be overlooked as potential sources. Collect a dip sample from the
cistern.
4.8 Other hot and cold water samples
If there are several bathrooms or wash hand basins be sure to collect samples representative of
the whole system and those outlets most likely to have been used by the patient. In any case be
sure to collect, at the very least, a sample from the outlets nearest to and furthest from the
hot water cylinder.
5. Other potential sources
Survey the property for other potential sources and collect samples from them. These might
include:
- The central heating system particularly if the patient had
worked on it in the two weeks prior to the onset of symptoms
- Spray bottles used to spray plants etc.
- Greenhouse humidification systems
- Indoor fountains
- Potting compost
- Spa pools
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