KWR recommendation leads to downscaling of standard for legionella

Ministerie I&W neemt advies over van KWR

In 2021, KWR and Berenschot handed over the report ‘Met recht naar een doeltreffender legionellapreventie’ to the Ministry of Infrastructure and Water Management. The report looked at whether the current legionella legislation as defined in the Dutch Drinking Water Directive is still in line with the latest scientific insights.

Focus on Legionella pneumophila

One of the recommendations in the report is that ‘priority institutions’ no longer need to monitor for all legionella strains and that they can concentrate exclusively on Legionella pneumophila. It is the most dangerous legionella strain, accounting for 90-95% of all reported cases of legionnaires’ disease in the Netherlands. Minister Mark Harbers of Infrastructure and Water Management recently informed the Lower House of Parliament that this recommendation will be adopted. That is a wonderful result in which research from KWR has had a concrete impact on day-to-day practice in the world of water.

Exception for hospitals and nursing homes

The reason for this change is the scientific insight that it is only in people with severely weakened immune systems that health can suffer from legionella strains other than L. pneumophila. The result that there is no evidence to prove that monitoring other legionella strains is a good indicator of the presence of L. pneumophila led to the recommendation in the report to drop a broad approach to screening. Screening of this kind often leads to a range of drastic measures to keep non-hazardous legionella strains out of the systems, even though the health benefits are extremely limited. The change in the standard will not apply to hospitals and nursing homes. ‘Here, we do recommend continuing the inclusion of all cultivable legionella strains in the monitoring,’ says KWR researcher Paul van der Wielen. ‘These institutions are home to relatively large numbers of people with severely compromised immune systems. That means you have to stay alert across the full range.’

Amendment to legionella legislation

Van der Wielen and his colleague Frank Oesterholt are proud that their recommendation in the report has been adopted in full. ‘This shows that the Ministry has a lot of confidence in the quality of our work,’ says van der Wielen. ‘Discussions about legionella legislation have been going on for over a decade. It is a good thing that we have now been able to provide convincing arguments demonstrating why it makes sense to amend the legionella legislation in this respect, making legionella prevention in mains water systems a lot more effective.’ Other recommendations from the report, including lowering the warm-water temperature of the boiler for the purposes of the energy transition, are still sensitive, van der Wielen says. ‘To back up this recommendation, KWR has launched an initiative as part of the Mission-Driven Research, Development and Innovation (MOOI 2022) scheme to work with a consortium of heat suppliers, engineering companies, technology suppliers, drinking water companies and industry associations. They will investigate whether, and with what innovative control measures, Legionella pneumophila can still be kept under control when the warm-water temperature is lowered.’

A detailed article on the change to the legionella standard can be read in H2O (in Dutch).