In developing countries, 80% of diseases are water-borne. However, the notion of ?zero risk? does not exist even in developed countries. The epidemic of Legionnaires' disease that broke out in Paris in June?July 1998 was a painful reminder of our vulnerability to these pathogens. Solutions to combat these problems nevertheless exist, consisting of a combination of hygiene, maintenance and disinfection of the installations.
The organisers of the football World Cup had anticipated the threat of terrorists and hooligans. Instead, they found themselves facing a bacteria of the family Legionella. In Paris, in July 1998, some twenty persons contracted Legionnaires’ disease, four of whom died.
Legionella is justly feared by water treatment engineers and those in charge of hot water or cooling systems. Over 500 cases of the disease are diagnosed each year in France, though the true number of people affected is thought to be over 2,000.
Water is the principal reservoir of the bacteria. Research has shown that lakes, rivers, etc. are the natural habitat of Legionella. These bacteria are capable of intracellular development in protozoa. They may also be transported by cysts of vagrant amoebas.
At the French National Public Health Network (RNSP: Réseau National de Santé Publique), they point out that “the sources of contamination incriminated in epidemics are usually those installations which favour the rapid multiplication of Legionella in the water and the production of aerosols”. The optimal temperature for development of the bacteria is 37 °C. Some types of installation are therefore particularly prone:
- hot water distribution channels supplying
showers,
- air-conditioning and cooling tower systems (the latter are thought to have been responsible for the Paris epidemic),
- pools used for relaxation, balneotherapy or thermal spring therapy, in which the hot water is raised to a temperature of over 30 °C and stirred up (whirlpool baths, etc.),
- medical facilities where respiratory conditions are treated using aerosols,
- thermal waters,
- decorative fountains.
Of all these potential sources, hot water distribution systems are the most frequent cause of infection.
Legionnaires’ disease was made notifiable in 1987, in order to be able to monitor the problem and rapidly implement preventive measures. However, in practice the system has proved rather ineffective and few cases are actually reported (less than 10 % in 1995).
As soon as the disease is identified, the bacterial reservoir has to be found.
The investigation covers all the patient’s activities during the 10 days prior to onset of the disease. Everything is methodically vetted and thoroughly examined.
Collecting a maximum amount of information
The information collected makes it easier to identify potential sources of contamination. An evaluation is carried out including a description of the establishment and the neighbourhood, as well as the domestic water network, air-conditioning installations, atmospheric cooling towers, etc.
For the domestic hot water network, for example, everything is examined: the method of production and any additional treatment, the distribution circuit, the quality of materials, water temperature in the tanks and at point of use. The cold water network has to be checked for inadvertent heating of the water in pipes passing through overheated parts of the building.
The study then goes on to conduct a complete ‘diagnosis’ of the environment. This allows the identification of critical points that need to be analysed in greater detail. These are points presenting a risk of multi-
The application or spread of Legionella. Particular attention is given to points from which domestic hot water is drawn and the bottom of storage tanks. In air conditioning installations, it is usually cooling battery condensates, moistening fluids and residual water in plumbing traps that pose the greatest risk. In cooling towers, it is the surface run-off. Samples are taken at all suspected points to test for the presence of bacteria.
Peripheral elements and enrichment by stagnation or swabbing will depend on the purpose of the test and the number of Legionella. Several sampling techniques can thus be used at points of use:
- - If the aim is to test for contamination at the point of use under normal conditions, the sample is taken from the first stream of water at the temperature of use.
- - If, on the other hand, the most unfavourable situation in terms of contamination is sought, sampling may be done after a period of stagnation (one night).
- - If the aim is to determine whether the network is contaminated upstream from the point of use, the sampling points are flamed and sampling done after the water has been allowed to run for some time.
- - Including the results of swabbing in the sample may be of interest in order to study
Sampling according to the rules
Sampling methods for water suspected of being contaminated with Legionella are laid down in the national health regulations. In France, the relevant document is DGS Circular No. 97/311. The sample consists of a litre of water placed in a sterile flask. If the sampled water has been treated with an oxidising biocide, the flask must contain sodium thiosulphate at 0.50 % to block the germicide action. The exact procedure followed in respect of localisation, flaming of
the ecology of the sampling point. This approach is recommended within the framework of installation surveillance, to evaluate the effectiveness of control and preventive measures. The swab must be introduced as far as possible into the tap or shower head and the sample taken with a repeated circular motion (approximately 4 times). The swab is then left in the corresponding water sample.
Whichever technique is used, the samples must be reproducible.
Ensuring reproducibility of samples
To be able to compare cases of contamination in space and time, it is important to establish detailed protocols for the persons responsible for taking the samples. For each sample, the records indicate the nature of the water being analysed (domestic hot water, condensates, etc.), the operations carried out (treatment, mixing, etc.), identification of the sampling point, and sampling date, time and conditions. The sample is stored in a refrigerated container at a maximum of 4 °C (but not frozen), and delivered to the laboratory within 48 hours for analysis.
Among the laboratories capable of identifying Legionella, those approved for the control of natural mineral waters have been the subject of intercalibration for the detection of this family of bacteria.
Testing for and quantifying bacteria are carried out in accordance with French standard AFNOR NF T90-431 (November 1993). This standardised method allows homogeneous results to be obtained with a sensitivity of 50 CFU/litre (CFU = colony forming unit). This degree of precision is sufficient to establish whether there is a health risk. To determine the density of Legionella, the analytical standard requires the filtrate to be recovered from 5 ml. The characteristics of some types of water (turbidity, etc.) sometimes means that filtration has to be carried out in several stages. Recovery can then only be undertaken in 10 ml. This operation modifies the detection threshold, which becomes 100 CFU/litre. The complete results (detection and quantification) are usually available in 8 to 10 days.
The results are interpreted taking into account the preliminary investigation of the network. They also serve as a reference to evaluate the effectiveness of the measures taken.
The environmental study should always be the subject of a written report indicating the main results and the measures envisaged to reduce the risk (closure, restrictions on activities or on the use of water, taking the premises or equipment out of service, cleaning, disinfection, maintenance and surveillance protocols).
Cleaning and disinfecting the network
Disinfection is only applied to something that is clean. The first thing is therefore to thoroughly clean all the elements of the network.
For example, for a hot water network, the following actions are needed:
- - remove and clean all the taps and fittings (shower heads, anti-splash nozzles, etc.) in an acidic pH solution followed by disinfection in a solution containing at least 50 mg of free chlorine per litre of cold water for at least 30 minutes,
- - change all the joints and filters,
- - empty, clean and descale the tanks, rinse the pipes. These operations are followed by disinfection, either by chlorine shock, with hyperchlorination of the tanks for 24 hours, or by thermal shock, raising the temperature of the network to an outlet level of 70 °C at all taps, to be maintained for 30 minutes.
The effects of these disinfection measures are of limited duration, and permanent measures therefore need to be put in place to avoid any rapid recolonisation. Some of these measures relate to maintenance: regular and effective maintenance will for example avoid the creation of biofilm and scaling. The experts recommend emptying, flushing, cleaning and disinfection of tanks, water-heaters and pipes at least once a year.
However, the effectiveness of the long-term control measures described above is related to the design of the network. For this reason, additional actions to eliminate design faults and improve the intrinsic safety of the installations are recommended. This can be achieved by having any unused pipe sec-
The case of swimming pools, spa tubs and Jacuzzis
Apart from pools used exclusively for functional reeducation in a medical context, the regulations relating to swimming pools and bathing areas instituted in application of the public health code apply to all pools used for bathing or swimming open to the public (even if privately owned). Whirlpool baths, spa tubs or Jacuzzis fall within the scope of these regulations if they constitute the only pool in a sports, leisure or relaxation establishment.
In the event of a pool being implicated in an outbreak of Legionnaires’ disease, the entire installation should be drained: water distribution networks, pool, etc. In the case of the pool, the procedure involves cleaning and disinfecting the bottom and sides, and washing and unclogging the filters coupled with thermal or chemical (chlorine) disinfection and even the replacement of the filter medium.
Depending on the results of the diagnostic investigation of the installation, modifications may be required (improvement of filtering and/or recycling of the water).
The regulation recycling time of 30 minutes, applicable to paddling pools, represents the maximum acceptable for whirlpool baths. Depending on the volume and the level of use, a whirlpool bath should be completely emptied 2 to 3 times a week, or even every day if necessary, but never less than once a week. The filter(s) should be disinfected on a weekly basis.
Disinfectant should be introduced upstream of the inflow into the pool (after the water has been filtered and heated), rather than directly into the pool. The disinfectant used must be on the list of those approved by the Conseil Supérieur d’Hygiène Publique de France. Of these, chlorinated products would appear to be preferable in view of the bacterial flora encountered. Care must be taken to use them at concentrations that are sufficient (regulatory levels) and stable over time. Furthermore, filtration and disinfection treatment should never be interrupted, even if the pool is not in use.
The level of disinfectant in the pool water needs to be checked several times a day as does the pH. In addition to the regulatory controls, compulsory bacteriological controls should include a test for Pseudomonas aeruginosa. This is a good indicator of a deterioration in the bacteriological quality of the water.
tions removed whenever plumbing work is carried out. An expert can be called in to carry out a complete evaluation of the work required.
Calling in an expert
The evaluation and the disinfection operations can be conducted by a competent service provider. Care is needed when choosing a firm to ensure that it is fully aware of the problems of bacteriological contamination and suitably equipped to carry out the diagnostic work. Nowadays, there are very few firms in the market. Apave, for example, states that it is “incapable of dealing with infectious risks of this type”. Socotec subcontracts the biological analysis component, but can carry out the network evaluation. Bureau Veritas is the only firm to state that it is suitably qualified to deal with all aspects of the problem. “We have adapted the HACCP (Hazard Analysis Critical Control Point) method, developed for the food industry, to testing for Legionella”, explains Gilbert Le Roux, Development Manager at Bureau Veritas. For a given network, as part of the diagnostic work, the firm identifies the strains of Legionella and the points that are contaminated.
If the network is contaminated it must be treated in order to kill off the bacteria. The evaluation report draws up a list of dangers and the main points that need to be monitored.
Here, too, it prescribes remedial actions, and prepares specifications for the sanitary follow-up procedures, which will serve as basic guidelines for actions taken by the client responsible for the work. Lastly, Bureau Veritas prepares a report on the results of its evaluation work before the installation is put back in service.
