Legionnaires' disease outbreak investigation toolbox

Specimen engineering designs for spa pools and associated water systems [1][2]

(Refer also to guidance on typical systems L8 Legionnaires' Disease guidelines Health and Safety Executive paper [3]. Other member states might have their own versions of such guides).

Where to sample in an installation - general guide

Sampling spa pools in an outbreak

• As a minimum always sample the pool and the balance tank (where fitted)
• Also consider sampling from jets and overflow grids
• When definitely incriminated, also consider biofilm samples from within pipes including air lines

Procedure

• For spa pools using chlorine or bromine-based systems, sodium thiosulphate is a satisfactory neutralising agent and 180mg/l is usually sufficient to neutralise up to 50ppm of chlorine. A mixture of lecithin and Tween 20 can be used to neutralise PHMB (Polyhexamethylene Biguanide), specific details and further advice should be sought from the testing laboratory.
• If other disinfection systems are in use, the testing laboratory must be informed before the sample is taken to ensure that the appropriate neutraliser is supplied, if an appropriate neutraliser is not available then the sample must be tested as soon as possible, the testing laboratory will need to take into account the time delay before testing is carried out when interpreting results.
• Sample bottles for microbiological testing should be either individually wrapped or disinfected by wiping with, for example, an alcohol swab before use.
• Bottles should not be rinsed with the water to be tested. To take the sample, the stopper or cap is first removed with one gloved hand making sure that nothing touches the inside of the bottle or cap.
• While the bottle is being plunged into the water the long axis should be kept approximately horizontal but with the neck pointing slightly upwards to avoid loss of the neutralising agent. The bottle is quickly immersed to about 200- 400mm below the pool surface, at which point the bottle is tilted upwards to allow it to fill. On removal from the water, the cap is immediately replaced, the sample shaken to disperse the neutraliser, and then sent to the laboratory without delay to enable analysis preferably on the same day and certainly within 24 hours of sampling. In transit the sample should be protected from light and placed in an insulated container maintained at approximately 2 - 8 ºC by freezer or ice packs. The sample container should not come in direct contact with the freezer packs. A record should be made of the pH value and the active disinfectant residual determined at the time of sampling.

This and any other relevant information should accompany the sample to the testing laboratory to enable appropriate interpretation of the results.

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