Legionnaires- Where’s the Trend?

The Statistics

Above are the figures released by gov.uk on the number of recorded cases of Legionnaires’ disease in the UK, between January 2015 and October 2017. As you can see, 2017 has not been a very good year. A very common trend is the summer months from June to October, the number peaks, with August, September and October having the highest number of cases.

There could be various reasons for this; ambient temperatures are higher during this period and favourable for bacterial growth; irrigation systems are in more use during the warmer months; overseas travel is common during this period.

Below are the figures in the same time period but with the regional data.

Statistically, London has the highest number of Legionnaires disease cases averaging at just fewer than 5 reported cases per month. London is realistically the most densely populated part of the UK.

The main reported cause of cases is from people travelling abroad (so there is some comfort for the UK in that manner). Cases acquired abroad are unlikely to receive further investigation; however, there have been discussions previously that use of our systems at home when we return from holiday could be a risk. There may be some potential for bacteria to proliferate in our home domestic systems for several reasons; we leave our systems unused and stagnant for 2 weeks with the immersion heater switched off; the water tank in the loft warms to a satisfactory temperature in the summer sun; we use the shower when we return from our holiday. The causation chain looks complete! This could perhaps be an area for further research.


The legionella risk assessment should take into account the different conditions systems will operate under i.e. the temperatures recorded from a cold water storage tank and system will differ by perhaps 10°C in the winter and summer, and make allowances for this. Or if an irrigation system is unused for the majority of the year, is it fit for purpose when it is required during the summer months?

If control is lost during the warmer months, as the statistics suggest, then the recommendations should compensate for this. Legionella risk assessments is what we do at Managed Water Services, call us if you need assistance.

by Managed Water Services