Published May 2024. This version replaces ‘Guidance on Legionella for Transient Sites’ which was published in 2018.

In 2019 over 500 cases of legionnaires disease were reported in England and Wales. Public Health England statistics indicate that historically between 7 and 12% of all cases proved fatal. In addition, unreported cases are thought to number between 4000 and 6000 infections each year. For those that recover, the disease is often debilitating with recovery taking between 12 and 18 months and survivors often left blind, deaf, or suffering from a loss of limbs due to complications.

The disease is contracted through inhaling aerosols of water containing the legionella bacteria. The bacteria proliferate at temperatures between 20°C and 45°C, within bodies of stagnant or slow-moving water and where nutrient sources are present. Once within the human lung, the number of bacteria increase significantly and produce toxins.

Within transient geotechnical or geoenvironmental sites, respirable water aerosols may be encountered associated with mobile welfare units, drilling mists, emergency showers, temporary water storage drums, dust suppression systems or jet washers. Transient sites have been defined as typically short duration workplaces or where mains water supplied welfare is not available.