Genetic analysis is key to understanding legionella risk, Edinburgh and Glasgow University scientists say

Routine analysis of water supplies and the genetic makeup of bacteria could be the key to identifying the source of Legionnaires’ disease outbreaks, researchers have said.

It could also inform public health measures to limit the spread of infection, according to a genomic study of the legionella bacteria that causes the disease.

Improved testing is crucial, scientists say, because the disease – a severe form of pneumonia – is contracted by inhaling the bacteria in tiny droplets of contaminated water.

Outbreaks are often linked to water systems in hotels, cruise ships and hospitals, and also within the community.

A team from the Universities of Edinburgh and Glasgow, Public Health Scotland and the Scottish Legionella Reference Laboratory compared the entire genetic code of more than 3,000 legionella samples found in patients and water sources, from both Scotland and around the world.

The results revealed “a new level of detail and fresh insights” into the characteristics of legionella and its transmission, the team said.

By analysing the genetic code, researchers found that legionella infections after travel were usually closely related to other variants from the same UK or international travel destination.

The analysis found that nearly one-third of infections in Scotland acquired in the community – not hospital or travel-associated – were caused by a single variant, which the team say should be “closely monitored”.

Different variants of the bacteria were found in some hospitals over a long period of time – up to 17 years in some cases – which suggests that the bacteria persisted or were repeatedly introduced into hospital water systems.

The team also found that there had been no reported cases of Legionnaires’ disease in any Scottish hospital in the past ten years.

They believe this is likely due to effectiveness of new control measures introduced during this time.

Professor Ross Fitzgerald, lead researcher from University of Edinburgh’s Roslin Institute, said: “Our study indicates that regular sampling of water systems and genome sequencing of legionella could be used to identify the source of new pathogenic variants before they become a clinical problem.”

The findings have been published in The Lancet Microbe, funded by the Chief Scientist Office, UKRI and Wellcome.