Legionnaires' Disease Outbreak in Murcia, Spain

Ana García-Fulgueiras, Carmen Navarro, Daniel Fenoll, José García, Paulino González-Diego, Teresa Jiménez-Buñuales, Miguel Rodriguez, Rosa Lopez, Francisco Pacheco, Joaquín Ruiz, Manuel Segovia, Beatriz Baladrón, Carmen Pelaz

Disclosures

Emerging Infectious Diseases. 2003;9(8) 

In This Article

Abstract and Introduction

An explosive outbreak of Legionnaires' disease occurred in Murcia, Spain, in July 2001. More than 800 suspected cases were reported; 449 of these cases were confirmed, which made this the world's largest outbreak of the disease reported to date. Dates of onset for confirmed cases ranged from June 26 to July 19 , with a case-fatality rate of 1%. The epidemic curve and geographic pattern from the 600 completed epidemiologic questionnaires indicated an outdoor point-source exposure in the northern part of the city. A case-control study matching 85 patients living outside the city of Murcia with two controls each was undertaken to identify the outbreak source; the epidemiologic investigation implicated the cooling towers at a city hospital. An environmental isolate from these towers with an identical molecular pattern as the clinical isolates was subsequently identified and supported that epidemiologic conclusion.

Legionnaires' disease (LD) has been an emergent disease since the 1970s. In the last few years, the increased use of a simple test for detecting urinary antigen Legionella pneumophila serogroup 1 in patients with pneumonia has facilitated diagnosis.[1] Transmission by aerosols has been extensively reported, and evidence of Legionella in aerosols derived from cooling towers has been provided.[2,3,4,5] Although a considerable body of epidemiologic evidence exists for the association of LD outbreaks with aerosols produced by cooling towers, some controversy exists about the role that cooling towers play in LD.[6,7,8,9,10,11,12,13]

We describe an explosive outbreak of LD that occurred in July 2001 in Murcia, a municipality with 360,000 inhabitants in southeastern Spain. We also report results of a case-control study performed to identify the source of this outbreak, which turned out to be a cooling tower. The outbreak of pneumonia was first detected on July 7. At the end of the first day of active surveillance, July 8, approximately 100 cumulative suspected cases were reported. More than 800 suspected cases were recorded by July 22, when the last case was treated, 2 weeks after the onset of the investigation. The epidemiologic investigation using a case-control study emphasizes a combination of strategies to measure and analyze an outbreak of LD that occurs in an area with many large potential sources of environmental contamination.

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