Some 80 out of 776 Dutch water purification plants risk spreading Legionnaires disease and must take preventative measures, health and safety watchdog RIVM has warned.

The advice is based on two earlier reports on the possibility that the plants, which purify waste water from industry and sewers, are the source of the legionella bacteria.

In 2018, some 600 people in the Netherlands caught the disease which manifests itself as pneumonia and can be deadly for the elderly and people in poor health.

The source of the contamination in most registered cases in the Netherlands is unclear, although likely culprits are jacuzzis and industrial cooling towers. A significant number of infections are picked up abroad, the RIVM said.

However, the watchdog found that in a number of cases dating from 2017 and 2018 the source of the disease were two water purification plants in the Netherlands.

In total, 80 plants are currently at risk of spreading the disease, particularly if the water in the basins is warm and air is blown into it. The droplets which then spread through the air can be breathed in by people, potentially making them ill.

The organisation recommends capping the water tanks or filtering the air around them by means of UV light to reduce the risk.