The 2012 Edinburgh Legionnaires' disease outbreak

Background
In the period between 28 May and 13 July 2012 a large outbreak of Legionnaires’ disease occurred in the South West of Edinburgh. An Incident Management Team (IMT) was convened, cooling towers in the areas were shot dosed, and clinicians and public alerted. The Scottish Government established their resilience room on 5 June.

Methods
Investigation included comprehensive assessment of cases including in-depth diaries and dates of onset, enhanced surveillance, environmental investigations, demographic and weather analysis. Immediate action involved sampling and disinfecting potential sources, active case finding, alerting primary care, reassuring the public and informing public health agencies across the UK.

Results
There were 56 confirmed and 36 probable and possible cases. Four deaths were reported, 49 patients hospitalised with 22 admitted to critical care. Over 1000 patients investigated and treated in primary care with 1626 urine and 572 sputum samples tested negative. Case mapping suggested that all were resident or had links to SW Edinburgh. Microbiology samples implicate Legionella pneumophila serogroup 1. Epidemiological and meteorological evidence suggested a common outdoor source in South-West Edinburgh over the duration 17 May to 6 June. Clustering of onset dates indicated a point source. Cases were 32–85 years, 73% males, likely to smoke and have underlying illnesses.

Conclusion
This outbreak is the largest in Scotland. Rapid multi-agency action and effective management of cases mitigated the effects of the exposure. Further investigations are on-going.