Most people do not become ill if they are exposed to Legionella bacteria. Some people have a higher risk of illness. If they inhale the bacteria, they could develop severe pneumonia. This often involves people over 60, people with chronic respiratory conditions (such as COPD), people with immune disorders and smokers. 

Causes of increase in reported cases

The increase in reported cases can be attributed in part to the fact that there are more older people. In addition, the increase seems to be associated with the spread of Legionella bacteria in outdoor are. Previous research showed that certain types of weather affect the spread of Legionella bacteria. One reason for this is that Legionella bacteria can survive longer in the air under humid, cloudy weather conditions. This allows them to spread over farther distances. Spikes in reported cases were particularly noticeable during heavy rainfall after a period of warm, dry weather.

Sources of water spray

People can become infected with Legionella bacteria if they breathe them in through very small droplets of water. These tiny water droplets (mist) can come from showering or using a hot tub, for example. Tiny droplets containing Legionella bacteria can also come from sources that spray a fine mist of water in outdoor air. This includes wastewater treatment plants, as well as ‘wet cooling towers’ which are used for air conditioning in large office buildings and hospitals. It is not yet clear how significantly these sources of outdoor water spray affect the number of people with pneumonia. More research is needed to determine that. 

Preventing exposure to Legionella?

Legionella prevention measures are required by law in some water systems, such as wet cooling towers and tap water systems in hospitals, hotels and swimming pools. There are rules in place to arrange that. 
It is very unlikely that anyone will become ill from exposure to Legionella bacteria at home. The following tips can help limit growth of Legionella bacteria in your home: 

• Set the hot water of the boiler or combi boiler to a temperature of at least 60 degrees.
• Do not set the boiler or combi boiler to ECO mode if you use hot water infrequently or only for short periods. In ECO mode, it takes a while for the water to reach peak temperature. It is important for hot water pipes to reach peak temperature for several minutes on a regular basis, for example while you are showering.
• Regularly clean devices that mist or spray water. This includes hot tubs, humidifiers or devices for sleep apnoea. Empty the device immediately after use. 
• Are you in your mid-60s or older, and/or do you have any chronic health conditions? Replace your shower head and hose every 2 to 3 years, and have your thermostatic tap cleaned.