Genetic research helps to explain why tracing the source of an outbreak of Legionnaires' disease that claimed four lives has proven to be more complicated than scientists hoped.

A DNA study of bacteria samples taken from patients infected during the 2012 outbreak in Edinburgh shows that it was caused by several subtypes of the bacteria.

The unexpected discovery means that tracing the source of this - and any future outbreaks - will be challenging, researchers say.

There were 92 confirmed or suspected cases during the outbreak in 2012 in addition to the four deaths.

In a bid to prove where the infection came from, attempts had been made to grow samples of Legionella - the bacteria that causes Legionnaires' disease - from water samples taken from the suspected source. Legionella is difficult to grow in the laboratory and attempts to do so during the Edinburgh investigation proved unsuccessful.

As an alternative approach, scientists led by the University of Edinburgh's Roslin Institute looked at the entire genetic code of bacteria samples taken from patients.

The team worked with colleagues from the University's Centre for Immunity, Infection and Evolution, the Royal Infirmary of Edinburgh and the Scottish Microbiology Reference Laboratories, NHS Greater Glasgow and Clyde.

They identified four subtypes of the bacteria that had probably existed at the source for many months before the outbreak, the scientists say.

The subtypes varied in their genes, which made some more likely to cause life-threatening symptoms of infection. Some patients were infected with more than one subtype.

These findings suggest that the severity of disease may be influenced by the bacteria itself, as well as known factors such as lung disease and smoking that make patients more susceptible to infection.

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Gene study helps explain Legionnaires' probe complications

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