Alan Wittle, the Chief Executive of the Basildon Univesity Hospital NHS Trust where two people have contracted Legionnaires’ disease is quoted by the BBC as saying, “We accepted some time ago the advice of experts that we will never be able to completely eradicate the bacteria, but we have worked hard to minimise the risk.” But is that true?

Once a building is collonised by Legionella bacteria - is it there forever? Whilst experts across the industry will certainly recognise that it can be very difficult to completely eradicate the bacteria, especially in a complex hot and cold water system, we would challenge the claim that it cannot be achieved. Some building owners go as far as replacing huge sections of pipework to remove regions harbouring the bacteria. There is no doubt that prevention is certainly easier than cure in these circumstances - but there are strategies available to deal with colonisation once it happens: the two most common approaches being the use of temperature and biocides to kill the bacteria. Killing and or flushing out planktonic bacteria (those ‘floating freely in the water’) using those approaches is generally very effective. The challenge comes in reaching bacteria burried within the biofilm (slime) where Legionella generally grow. Chemicals, at levels which are safe to use in domestic water systems, can struggle to permeate the biofilm and heat will often not be able to reach all parts of the system especially if there are dead legs, redundant pipework or rarely used outlets. Indeed ’shock treating’ systems with biofilm in them can actually free up surface material temporarily increasing the concentration of bacteria at taps and showers and possibly increasing the potential for infection.

The real challenge for hospitals though is that they can’t simply decide to close a ward, building or potentially a whole hospital for several days or weeks the way that a hotel or leisure centre might chose to - because sick people won’t get treated, patients won’t get life saving surgery and its very likely that many people will suffer or even die as a result. The hospital therefore has to balance this risk against the risk that a small number of people might get ill (or die) from Legionnaires’ disease.

If you can’t completely eradicate the bacteria from the water quickly, can you eliminate the risk of exposure? Point of use filters like those supplied by Pall can be fitted to all taps and showers within a collonised building making it essentially impossible for a user of a water outlet to be exposed to Legionella bacteria. They’re not normally intended as a long term fix - but they do offer a short to medium term fix whilst working out and validating the chemical or engineering solution, or waiting for a suitabe gap in schedules to enable invasive engineering work.

We worry that duty holders are accepting that you can never completely eliminate risk and confusing this with never being able to bring a collonised system back under control. Achieving the minimum level for regulatory compliance is not the same as minimising risk.