42 questions on Legionnaires’ disease

Below you will find an overview of frequently asked questions on the legionella bacteria and the corresponding answers. This information is intended for those organisations and authorities which distribute information about the legionella bacteria.
In addition to this information the Ministry of Health, Welfare and Sport and the Ministry of Housing, Spatial Planning and the Environment have published a brochure for the public containing the 25 most frequently questions on Legionnaires’ disease. This brochure can be obtained from post offices, libraries and the distribution centre of the Ministry of Housing, Spatial Planning and the Environment (telephone number +31 (0)79-3449449, distribution number 22668). The brochure is only available in Dutch.

This information is compiled by the Ministry of Health, Welfare and Sport and the Ministry of Housing, Spatial Planning and the Environment in association with the Ministry of Social Affairs and Employment, the Association of Dutch Water Companies (VEWIN), the Dutch Consumers’ Union (Consumentenbond), whirlpool bath companies, the Association of Provincial Authorities (IPO) and the West-Friese Flora (the Dutch flower market where the major outbreak of Legionnaires’ disease occurred in March 1999). The questions and answers have been categorized.

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Contents

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1 Definition and symptoms of the disease

2 Questions relating to the home situation (of private individuals)

3 Questions regarding public swimming facilities/saunas/whirlpool baths and large-scale public events

4 Questions with regard to being infected whilst on holiday

5 Questions regarding drinking water supplies at public places

6 Questions regarding whirlpool baths

7 Risks in the workplace

8 Other questions

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Disease and symptoms of the disease

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What is ‘Legionnaires’ disease’?
‘Legionnaires’ disease’ is a disease caused by the legionella bacteria that can lead to pneumonia. There is also a milder form of Legionnaires’ disease: legionella fever. ‘Legionnaires’ disease’ does not occur often. The disease is not new. It was identified in 1976, when a pneumonia epidemic occurred during a convention for war veterans of the American Legion in Philadelphia (USA). Every year around 45 cases are reported in The Netherlands; about half of the patients become infected while abroad.

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Where does the legionella bacteria occur?
The bacteria causing the disease can be found in very small quantities in the ground, and in water and tap water. The legionella bacteria becomes a problem when it is able to multiply, e.g. in water with a temperature between 25o and 55o Celsius that is stagnant for a long period of time. A strong flow can prevent the growth of the bacteria, but if this flow is not constant throughout an entire hot water system, water could become stagnant in certain spots (so-called dead corners), where further growth could occur, creating a risk.

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What are the symptoms of Legionnaires’ disease?
The period between being infected with the bacteria and the first symptoms of the disease (the incubation period) is approximately two to ten days. The disease starts with rapid-onset headaches, muscle pains and feeling generally unwell, followed by pneumonia with a high fever of over 39o Celsius. The patient coughs and is sometimes short of breath. Some patients suffer from vomiting and diarrhoea. The disease can have serious consequences, but can be treated effectively by immediate administration of the right antibiotics.

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What are the symptoms of legionella fever (the mild form)?
For two to five days the patient will experience mild flu-like symptoms such as fever, headaches, muscle pains and coughing. It cannot really be distinguished from other kinds of flu. This mild form of the disease is not dangerous, the symptoms can pass without further treatment.

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What is the treatment for Legionnaires’ disease (the ‘severe’ form)?
This disease can be treated effectively. Recovery is possible if the right antibiotics are administered immediately; these antibiotics can be prescribed by any doctor. It will take several weeks before the patient recovers. The sooner the treatment is started, the better. If Legionnaires’ disease is not treated correctly or promptly it can be fatal.

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How is infection transmitted?
Infection occurs through the lungs. It is assumed that the infection is transferred by inhaling the bacteria in droplets of water suspended in the air (misting). The disease is not contagious; it cannot be transferred from one person to another. Pets cannot become infected.

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2 Questions regarding the home situation (of private individuals)

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Is it still safe for me to take a shower?
Yes, it is. Legionnaires’ disease can easily be prevented. The bacteria can multiply in hot water pipes and hot water systems with a storage tank (such as boilers and certain types of combination boilers). If the temperature of this water is between 25o and 55o Celsius, the legionella bacteria can grow. At temperatures higher than 60o Celsius the bacteria will no longer grow, so the temperature of your hot water system needs to be set to at least 60o Celsius. There is no risk at all if you have a geyser; this system does not have a storage tank, so the bacteria will not get the chance to multiply.

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Is there a risk of being infected via the tap; for example while doing the dishes?
There is no risk if you have a geyser or if the temperature of your boiler or combination boiler is set to at least 60o Celsius (see here as well).

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Is there a risk of infection when using a coffee-maker or steam iron?
There is no risk. Coffee-makers and steam irons work with temperatures considerably higher than 60o Celsius, which make it impossible for the bacteria to grow.

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Is it safe to use a plant spray if it has been on the windowsill (in the sun) for some time?
We strongly recommend that you drain the water from the plant spray after use and refill it before using it again.

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What about the water reservoirs of central heating radiators?
These are harmless; although vaporization occurs, there is no formation of droplets and/or mist. However, regular cleaning of these water reservoirs with chlorine is recommended.

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What about the humidifiers in my home?
Humidifiers that work through vaporization do not pose a risk, as there is no mist. However, humidifiers that do create a mist could present a risk. This risk can be prevented by cleaning the water reservoir(s) and sprays with chlorine every week.

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I have read some articles about solar boilers in the newspaper. The temperature in this type of water heater is only 45o Celsius. Is there a risk of being infected with Legionnaires’ disease?
Due to the constantly changing temperature in the storage tank of the solar boiler and because the water in the central-heating boiler is at all times heated to 60o Celsius, the origin and growth of the bacteria is effectively prevented. Or in other words: solar boilers pose no risk of infection with the legionella bacteria, providing they are correctly installed and adjusted by a recognized or accredited installer. The installation of a new drinking water supply needs to be done by a recognized installer or installation company, as they work in accordance with the guidelines laid down by the Association of Dutch Water Companies (VEWIN).

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Could the air conditioning in my car cause a problem?
Since these systems do not create a mist, there is no risk from the air conditioning in cars.

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Am I at risk if I use the sprinkler in the garden to water my lawn?
If cold tap water is used, there will not be any risk; the temperature in this kind of system will rarely reach or remain above 25o Celsius for a prolonged period of time. However, if you are using a (flexible) garden hose that has been in the sun for a long period of time, is not used often and contains stagnant water, then there is an increased risk of bacterial growth. It is important to completely drain the garden hose after it has been used. This kind of heating will not happen if the system is buried underground.

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I installed an outdoor shower in my garden. The water comes from a garden hose, which lies on the lawn. During the day the water in the hose is heated by the sun. When the shower starts, warm water comes out at first, followed by the cold water. Is there a risk of being infected?
Generally speaking the risk is very small. The temperature in this kind of system will rarely reach or remain above 25o Celsius for a prolonged period of time. There is absolutely no risk if, after use, the water is drained from the shower head and the garden hose, so that there is no stagnant water in which the legionella bacteria can develop. However, if you are using a (flexible) garden hose, that has been in the sun for a long period of time, is not used often and contains stagnant water, there is an increased risk of bacterial growth. To prevent any risk we advise you to make sure these hoses and systems are drained after use.

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I have a small pond with a fountain. This produces a mist and during hot summers the water can get quite warm. Am I in any danger?
Generally speaking the risk is very small. It is unlikely that the temperature in the pond will stay above 25o Celsius for a week. In addition, the pond also contains other bacteria and organisms alongside any legionella bacteria. These will prevent significant growth of the legionella bacteria.

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Could the Water Board (waterleidingbedrijf) not remove the bacteria from the water? That way they will not be present in the drinking water and I should not have to worry about misting.
The water supplied by the Water Board is of such quality that no pathogenic amounts of bacteria are present. However, it is always possible that a number of bacteria remain. Their numbers are so small that is technically impossible to measure them. The legionella bacteria are only occasionally present in cold water and do not constitute a public health risk. They only become a problem if the right temperature has not been set for warm water in a hot water system, allowing them to multiply.

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What is the risk of being infected in my private swimming pool?
There is no risk if the swimming water is chlorinated and circulated correctly (in accordance with the instructions of the supplier or installer). For showers at the swimming pool the same applies as for all other showers, hot water pipes and hot water systems: a minimum temperature of 60o Celsius for the water in the boiler or flushing with water heated to at least 60o Celsius every week.

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What can I do personally to prevent infection with the legionella bacteria?
You can take the following precautions:
1) After being away for a few weeks you can clean the water supply by flushing the shower with hot water only, while leaving the door open for ventilation. This way the water supply will be cleaned.
2) You can also check if the temperature of your boiler or combination boiler is set to at least 60o Celsius. Geysers do not present a risk.
3) Clean your whirlpool bath in the correct manner by cleaning the pumps and filters with special disinfectants used for cleaning private swimming pools. These disinfectants can be bought from companies selling whirlpool baths or private swimming pools, and at larger garden centres.

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Is it possible for me as a private individual to have water samples checked for the presence of the legionella bacteria?
Yes, this can be done by the same laboratories that are used by the Water Board (waterleidingbedrijf), like KIWA or a specialised consultancy agency. This will only be necessary if you are concerned about the hot water system, for example, when it has broken down.

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3 Questions regarding public swimming facilities/saunas/whirlpool baths and large-scale public events

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Is there a risk of infection during a visit to a (tropical) swimming pool?
Swimming pools do not represent a risk if the regulation amount of chlorine is added to the water. For information on using showers at swimming pools, please see here.

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Is there a risk of infection during a visit to a sauna?
If the correct precautions are taken, saunas pose a negligible risk. All saunas affiliated to the Dutch Sauna Bath Association (Nederlandse Saunavereniging) do everything in their power to prevent infection with the legionella bacteria. They ensure they have good working equipment for their saunas and whirlpool baths, and have this checked monthly. You can obtain the results of these checks at the reception desk of the sauna facility.

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Which parts of a swimming facility present a risk of infection?
The parts that are insufficiently chlorinated and disinfected pose a risk. Shower water is never chlorinated: showers create an increased risk if the water temperature in the pipes and shower heads is lower than 60o Celsius before it is mixed with cold water. This is especially the case in showers with a push button system. Whirlpool baths could also pose a risk in public places like these. It is important that these baths have a proper system for disinfection in place in accordance with the manufacturer’s regulations. For your own safety you could make inquiries about this with the manager of the sauna or swimming pool.

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Should I be extra careful when visiting a (flower) exhibition or botanical garden?
The risk of infection at a flower exhibition is no greater than at any other event, and ever since the Legionnaires’ disease epidemic at the flower exhibition in Bovenkarspel in March 1999, the Inspectorate for Health Protection and Veterinary Public Health (Inspectie Gezondheidsbescheming, Waren en Veterinaire Zaken), the municipalities and the provinces carry out many more checks.

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4 Questions with regard to being infected whilst on holiday

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What is the current situation abroad?
‘Legionnaires’ disease’ also occurs in other countries, and the risks are greater in areas with higher temperatures. We recommend taking the same precautions as you would in The Netherlands. If upon your return you experience symptoms such as those described under ‘What are the symptoms of legionella fever (the mild form)?’, please contact your doctor.

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Are there any steps I can take personally to prevent possible infection with Legionnaires’ disease at camp sites or hotels?
Although showers at camp sites do constitute a risk, in practice this risk is small. The washing facilities are used when the temperature is still relatively low, so the water temperature in the pipes will not have reached 25o Celsius. If you are concerned, it might be wise to let the tap run for a while to flush the pipes. At ‘bigger’ camp sites it could happen that at the beginning of the high season a shower block, that was previously closed, is opened. Be aware that in such circumstances the water temperature could have reached more than 25o Celsius. In France, a minimum temperature of 60o Celsius is compulsory for boilers at camp sites. If the pipes feeding a tap are above, or just below, ground level, this could also create a risk, as the outside temperature could mean that the water in those pipes is heated to between 25o and 55o Celsius. This risk increases if the tap is not used that often. In that case we advise you to get water from a tap as close to the main pipe as possible. Some campers tend to install a shower at the camp spot; for example by hanging a water bag from a tree with a shower head attached. This bag will be in the sun for days allowing the legionella bacteria to grow. We strongly advise against this. Hotels in The Netherlands need to ensure they have a safe water supply system; this is monitored by the Inspectorate for Health Protection and Veterinary Public Health (Inspectie Gezondheidsbescheming, Waren en Veterinaire Zaken). If you want to be on the safe side, you could cleanse the water supply by flushing the hotel shower with hot water only, leaving the door open for ventilation.

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I own a boat/caravan/camper van with a drinking water supply and a shower. How can I prevent infection with the legionella bacteria?
If you own a boat/caravan/camper van with a boiler, we advise you to check the temperature of the hot water coming from the tap. If this water stays well below 60o Celsius, we recommend you contact your caravan dealer or the supplier of your boiler. If you have not used the boiler for a long period of time, we recommend you drain the boiler and flush the boiler and pipes before use. The water in caravans and camper vans rarely remains in the water tanks and pipes for a long period of time, so the temperature will almost never get above 20o Celsius. In addition, there will be no mist, except when using the shower. We advise you to drain the tanks and pipes, and flush them with large amounts of water after the winter break or if the water has not been used for more than a few days. If the camper van, boat or caravan will not be used for a while, it would be best to drain the tanks and pipes. If you want to be absolutely sure, you could consider using chlorine or other disinfectants used for cleaning private swimming pools (for sale at specialist shops and larger garden centres), to flush out the pipes. Make sure you rinse everything thoroughly.

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5 Questions regarding drinking water supplies at public places

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I am responsible for the drinking water supply at a public place (hotel, swimming pool etc.). Who can I contact to make sure the installation does not present a risk?
Despite the care that goes into their installation, it could happen that large hot water systems at public facilities, hotels, camp sites etc. do not function properly due to:
1) the temperature being set too low;
2) insufficient circulation in branch pipes;
3) malfunctioning thermometers resulting in inaccurate temperature settings;
4) malfunctioning pumps;
5) visual contamination of the water in the hot water system; installations with long outlet pipes
6) installations with a lot of heat loss.
In addition to the recommended temperature setting of 60o Celsius, the amount of nutrient in the pipes is of importance when it comes to large drinking water installations (in contrast to the hot water systems at private residences). This is why it is vital that the installation is kept clean. For more information on taking water samples, their analysis, and advice on drinking water installations, please contact the Water Board (waterleidingbedrijf), KIWA or a specialised consultancy agency, such as the Netherlands Organization for Applied Scientific Research (TNO). They advise companies, monitor water temperature and can grow cultures. Owners are responsible for their drinking water installations.

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6 Questions regarding whirlpool baths

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I own a whirlpool bath. Is it safe for me to use it?
If the whirlpool bath is connected to a hot water system and pipes, in which a temperature of at least 60o Celsius is maintained as far as the whirlpool bath taps from which the bath is filled, there is no risk at all. It does not make a difference if the whirlpool bath was built-in or if you built it yourself. The type of whirlpool bath (air or water injection) is also not relevant. If the whirlpool bath is drained after every use it will not be necessary to disinfect the bath. Cleaning the bath properly with household cleaning products, such as chlorine, is a standard measure, and would also be advisable in this case.

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I own a whirlpool bath that is drained after use. Am I in any danger?
The risk from such a whirlpool bath lies in the hot water supply and the hot water system itself. If they are working properly and if they reach a temperature of at least 60o Celsius which is maintained as far as the whirlpool bath taps, there is no risk at all.

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Should I be extra careful if the whirlpool bath has not been used for a long period of time?
In such circumstances we advise you to fill the bath with water heated to 60o Celsius, to turn on the bath for about five to ten minutes and to drain the bath afterwards. Another method is to disinfect the bath with disinfectants and cleaning agents for swimming pools, which can be bought at, for example, installation companies. You could also ask the supplier of your whirlpool bath which products can be used.

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If the bath and pipes are dry after use, is there still a risk?
If the whirlpool bath is built in such a way that the circulation pumps are also dry after use, the risks, even if the bath was not used for a long period of time, are still smaller than with a bath that is not drained after use. To rule out any risk we advise you to fill the bath before use with water heated to at least 60o Celsius and to turn on the bath for about five to ten minutes. Another method is to disinfect the bath using the appropriate cleaning agents. This way any legionella bacteria, which despite all precautions have been able to multiply in the pump and pipes, can be reduced to very low concentrations.

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Could I have my whirlpool bath checked for the presence of Legionnaires’ disease? Is there a measuring instrument that I can use to do this myself?
Carrying out an inspection for the legionella bacteria is not possible without extensive
laboratory testing. If you would like to get the water from your bath checked, please contact the Water Board (waterleidingbedrijf), KIWA or a specialised consultancy agency.

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Who is responsible for the prevention of Legionnaires’ disease in my bath?
You are responsible for the prevention of Legionnaires’ disease in your own bath. If you have concerns about your hot water system, whirlpool bath etc., we advise you to contact the installer or the Water Board (waterleidingbedrijf).

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I own a whirlpool bath that needs to be filled with water that is not drawn from a hot water source with a temperature of 60o Celsius. Is there a risk of being infected with Legionnaires’ disease?
If you disinfect the water in the whirlpool bath with chlorine, such that the percentage is 0.5 mg/litre free chlorine, and the pH value is between 6.8 and 7.8, there is no risk. When the bath is not being used, it would be wise to disinfect the bath and the pipes, and to check the pH value. You can use disinfectants and cleaning agents for swimming pools, which can be bought from, for example, installation companies.

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I own a whirlpool bath from which the water is not drained after use. Could the legionella bacteria multiply in this?
If the whirlpool bath is connected to a hot water system and pipes, in which a temperature of at least 60o Celsius is maintained as far as the whirlpool bath taps, there is no risk at all. The bath must be filled with water from those taps. In addition, the water in the bath must be disinfected with a minimum of 0.5 mg/litre free chlorine (this should also be done when the bath is filled with water cooler than 60o Celsius). The pH value of the water must always be between 6.8 and 7.8. When the bath is no longer in use, it would be wise to disinfect the bath and the pipes, and to check the pH value. You can use disinfectants and cleaning agents for swimming pools, which can be bought at, for example, installation companies.

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I am the manager of a swimming pool which also has a whirlpool bath. What requirements must the whirlpool bath fulfil to prevent the legionella bacteria from multiplying?
The bath water must be disinfected with a minimum of 0.5 mg/litre free chlorine. The pH value of the water needs to be between the range of 6.8 to 7.8. Due to the generally higher temperatures and the movement of the water caused by air and/or water injections, chlorine vaporization will occur. In addition a pH change will occur due to the limited buffering capacity of these smaller baths, so the chlorine will be less effective in disinfecting.
As these whirlpool baths are generally used more often (more people in each than in regular pools) the chlorine usage is also higher, so it is important to carry out regular checks on the chlorine content and the pH value.

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7 Risks in the workplace

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Who can I turn to as an employer or employee with questions regarding the health risks in the workplace?
In accordance with the Dutch Occupational Health and Safety Act (Arbowet) an employer must carry out a risk assessment and evaluation to determine whether employees could encounter health risks. Subsequently, the employer must carry out measures to eliminate these risks. An employer or employee can contact the working conditions services (Arbodienst), if he is worried about possible legionella infection. Every employer is obliged to provide such a working conditions service.

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Is there a greater risk of infection for people working in greenhouse farming, horticultural or other professions?
People working in greenhouse farming or horticulture are not at greater risk of being infected with Legionnaires’ disease. The Healthcare Inspectorate (Inspectie voor de Gezondheidszorg) came to this conclusion after looking into the number of cases of Legionnaires’ disease in the last five years. Those numbers also showed that other professions are not at greater risk. Even though Legionnaires’ disease is not always diagnosed, an increased risk associated with a certain profession would have been identified by the cases reported at the Inspectorate. It is therefore very unlikely that the disease claimed any victims in the greenhouse farming and horticulture industries without this being noticed. Data from Stigas Arbodienst, the national working conditions service for the agricultural industry, has also not indicated a heightened risk. Greenhouse farming uses basins in which rainwater is collected. This water is used for techniques using drops of water or a mist. In the Dutch climate the temperature of the water will stay below 20o Celsius most of the time, and only during extremely warm weather will it reach above 20o Celsius. Since the legionella bacteria can only multiply in stagnant water at temperatures between 25 o and 55o Celsius, under normal circumstances the bacteria will not constitute a risk. Some greenhouse farmers or horticulturists use ditchwater or surface water for these techniques; the same applies for these types of water.

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What happens during the hosing down of spaces using a high-pressure spraying pistol which often causes a large amount of vapour?
High-pressure spraying pistols with hot water or steam are fed with cold water. The heating itself takes place inside the spraying pistol, which has a high flow rate. The combination of these two factors prevents multiplication of the legionella bacteria. This means that the mist from high-pressure spraying pistols does not contain the legionella bacteria. High-pressure steam cleaners generate steam at such high temperatures, that any legionella bacteria are killed. The steam therefore does not contain the legionella bacteria. Cold water high-pressure spraying pistols obviously constitute no risk.

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8 Other questions

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I live in a nursing home/have been admitted to hospital; is it safe for me to take a shower?
Hospitals and nursing homes must comply with the advice of the Health Counsel of the Netherlands (Gezondheidsraad). The Healthcare Inspectorate (Inspectie voor de Gezondheidszorg) has pointed this out to them on many occasions. The advice explains how Legionnaires’ disease can be prevented. In addition, the government ensures that management plans are in place and complied with at public facilities with a water supply system. If you would like more information about the maintenance of the drinking water system, please contact the responsible employee at the nursing home/hospital.

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This is a joint publication of the Ministry of Health, Welfare and Sport, PO Box 20350, 2500 EJ, The Hague, The Netherlands (www.minvws.nl) and the Ministry of Housing, Spatial Planning and the Environment, PO Box 20951, 2500 EZ, The Hague, The Netherlands (www.minvrom.nl) in association with the Ministry of Social Affairs and Employment, the Association of Dutch Water Companies (VEWIN), the Dutch Consumers’ Union (Consumentenbond), whirlpool bath companies, the Association of Provincial Authorities (IPO) and the West-Friese Flora (the Dutch flower market where the major outbreak of Legionnaires’ disease occurred in March 1999). This publication is for information purposes only, and no rights can be derived from the information contained in it.