Legionnaires' disease outbreak in Murcia, Spain

Area of Science:

• Public Health
• Infectious Diseases
• Epidemiology

Background:

• Legionnaires' disease is a severe bacterial pneumonia caused by Legionella.
• Outbreaks can occur when contaminated water aerosolizes, leading to widespread exposure.
• Identifying outbreak sources is critical for public health interventions.

Purpose of the Study:

• To investigate the cause of a large Legionnaires' disease outbreak in Murcia, Spain, in July 2001.
• To identify the specific source of the outbreak through epidemiologic and microbiologic methods.
• To confirm the implicated source through molecular analysis.

Main Methods:

• Conducted a large-scale outbreak investigation, including 600 epidemiologic questionnaires.
• Performed a case-control study matching 85 patients with two controls each.
• Collected environmental samples, specifically from cooling towers, for microbiologic analysis.

Main Results:

• Confirmed 449 cases of Legionnaires' disease, with a 1% case-fatality rate.
• Epidemiologic data indicated an outdoor point-source exposure in the northern part of Murcia.
• Cooling towers at a city hospital were implicated, and environmental isolates matched clinical isolates.
• Identified the largest Legionnaires' disease outbreak globally to date.

Conclusions:

• The cooling towers of a city hospital were definitively identified as the source of the 2001 Murcia Legionnaires' disease outbreak.
• The investigation highlighted the importance of environmental surveillance and rapid response in controlling large-scale infectious disease events.
• This outbreak underscores the potential for Legionella transmission from engineered water systems.