Do you have any questions? Below you will find the most frequently asked questions


What is Legionella?

Legionella pneumophila is an aerobic gram-negative bacterium. 39 different species of Legionella have been identified. The most common Legionella species is Legionella pneumophila. Legionella pneumophila species appear in most natural water supplies like lakes, ponds and rivers in low concentration and in dormant stage. But Legionella bacteria from natural habitats can be increased remarkably in man-made hot water systems where the temperature is optimal for their growth and can reach a dangerous concentration. Therefore, to obtain more energy efficient and healthy domestic hot water systems, it is necessary to look at the interactions between Legionella pneumophila bacteria and the domestic hot water system.

What are the symptoms of a Legionella infection?

Legionella pneumophila is the most dangerous Legionella species for humans, it is able to induce two kinds of illnesses that appear two to ten days after exposure. One is Legionnaires’ Disease, a life threatening pneumonia against which the victim requires urgent medication. Symptoms of Legionellosis are a general ill feeling, headache, muscle pain, cough and shortness of breath, followed by pneumonia with a fever of over 39°C. Legionellosis must be treated with antibiotics, and even after the infection, the disease can have long-lasting consequences. The other disease caused by the species is Pontiac Fever, named after an outbreak in Pontiac, Michigan in 1968. This variant is an flue like acute respiratory disease. Having Pontiac fever, the patient will experience mild flu-like symptoms for 2 to 5 days, such as fever, muscle pain, headache and cough. The disease is not dangerous in this mild form, there is no pneumonia. The complaints can pass without treatment. It was only after 1976, after the outbreak in Philadelphia, where Legionella was discovered, that public health officials were able to ascertain that the same bacterium caused the previous outbreaks of Pontiac Fever.

When is Legionella discovered?

The Legionella bacterium delivers its name from an outbreak at the American Legion’s Convention at the Bellevue Stratford Hotel in Philadelphia in July 1976. 221 American Legion Members were struck with severe pneumonia, of whom 34 died. This form of pneumonia was called Legionnaires’ Disease and when the bacterium causing it was finally identified, it was termed Legionella. It was not the first outbreak. It is known from stored tissue that this bacterium was responsible for mystery illnesses 50 years ago. Prior to 1976 there had been an outbreak in the St. Elizabeth’s Hospital in Washington DC where 81 patients became ill, 14 of whom died. Another outbreak in the same Bellevue Stratford Hotel in Philadelphia was in 1974 at an Oddfellows Convention where 20 attendees got ill, two of whom died.

How common is a Legionella infection?

Legionella appears in the media occasionally, this does not happen often. Fire and CO poisoning are well known as causes of building related deaths. But, more people die each year from Legionella infection than from CO poisoning. A Legionella infection often goes unnoticed, as it can manifest as a mild flu or serious pneumonia. As a result, the cause is often not detected, so the registered number of Legionella infections remains low. However, a urine test can confirm a Legionella infection.

How do you get infected?

A big misunderstanding is that you get a Legionella infection by drinking contaminated water. This is not true. Legionella bacteria cannot survive in the human stomach. Drinking tap water therefore does not present any contamination risk. If that is the case, how do you get infected? Infection occurs by inhaling contaminated aerosols, aerosols are very small water droplets that are produced by, for example, a shower head. These drops are so small that they can enter the lungs. Please note that steam/vapour cannot contain Legionella bacteria as these drops are too small to carry bacteria.

Legionella in buildings

How does Legionella enter the building?

Legionella is naturally present in lakes, rivers and also in our tap water. The bacterium enters the building at a very low harmless concentration. However, in buildings there are situations that are optimal for the growth of the bacteria, such as ideal temperatures between 20 and 45°C or standing water. In this way dangerous concentrations can be achieved in buildings.

What can you do at home?

At home there are 2 things to look out for. First and foremost, the boiler temperature must be set at 60°C. At a temperature of 60°C, it takes 5 minutes to kill 90% of the Legionella bacteria present. Secondly, you should let the cold and warm water run for a few minutes at infrequently used taps if you started using these taps. Do the same when returning from a vacation.

Do you have to take measures at home after a holiday?

When you return home after a holiday of more than a week, it is best to flush your pipes. This for both cold and hot water pipes. Put your tap on the hottest setting to flush the hot water pipes. If the water from the tap is hot, let the water flow for at least a minute to remove the standing water. At a temperature of 60°C it takes 5 minutes to kill 90% of the Legionella bacteria present. You should ventilate the room while doing this.

Can Legionella also occur in a humidifier?

A humidifier with evaporation does not pose a risk because there is no aerosol development due to water atomization. However, humidifiers with atomization do pose a certain risk, especially when the water in the water reservoir heats up due to, for example, the sun.

Can you get sick from venting a heating system, as this also releases aerosols?

No, the water in heating installations is in a closed circuit. Legionella bacteria do not have enough oxygen and nutrients to survive for a longer time.

Legionella legislation

What is the BBT (2017)?

BBT is the Best Available Techniques for Legionella Control manual. This manual describes the technical guidelines for Legionella control to which a sanitary installation is deemed to conform. The guidelines in this manual are seen as the code of good practice. The Agency Zorg en Gezondheid uses this manual as a reference document when exercising its supervisory function regarding compliance with the Flemish Legionella Decree of May 4 2007. You can download the manual via the link below:

What alternative measures for Legionella control are allowed?

In addition to the standard measure of temperature control (60°C departure, 55°C return), alternative control measures are also possible. Those measures must be approved by the minister. There are currently 7 approved systems (Ecodis® cell, Oxiperm®Pro, BIFIPRO®, Huwa-San Controller®, Aqualitybox®, Bello Zon®, EasyDis®). For each system, a ministerial decree containing a brief description of the device and the use conditions has been drawn up after a trial phase has been completed and after the advice from the Superior Health Council.

Legionella disinfection consultancy, advice and R&D

Legionella research, why does LoWatter work with a simulation model?

Daily research is carried out at UGent to gain better understanding in Legionella risks. Measuring Legionella is a very labor and time intensive process, resulting in the development of a simulation model that allows to predict Legionella contamination risk in a building. In this way, the cause of the contamination can be quickly determined in a contaminated building.

Isn't producing water at 60°C very energy consuming?

To be Legionella safe, we have to produce water at 60°C, while we only use temperatures around 40°C at our taps. This hinders the use of energy-efficient production systems (such as heat pumps) for the production of hot water. Producing water at those high temperatures therefore entails a lot of extra energy use, in contrast to the demand from consumers to work at a lower temperature. Ghent University is conducting research to provide a solution to these continuously high temperatures, so that energy can be saved without endangering human health.

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