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Results from theNational Legionella OutbreakDetection Program,the Netherlands, 2002–2012Jeroen W. Den Boer, Sjoerd M. Euser, Petra Brandsema, Linda Reijnen, Jacob P. BruinIn 2002, the National Legionella Outbreak Detection Programwas implemented in the Netherlands to detect andeliminate potential sources of organisms that cause Legionnaires’disease (LD). During 2002–2012, a total of 1,991patients with LD were reported, and 1,484 source investigationswere performed. Of those sources investigated, 24.7%were positive for Legionella spp. For 266 patients with LD,105 cluster locations were identified. A genotype match wasmade between a strain detected in 41 patients and a strainfrom a source location. Despite the systematic approachused by the program, most sources of LD infections during2002–2012 remained undiscovered. Explorative studiesare needed to identify yet undiscovered reservoirs andtransmission routes for Legionella bacteria, and improvedlaboratory techniques are needed to detect Legionella spp.in clinical samples with a high background of microbial florasuch as soil.Legionnaires’ disease (LD) is an acute pneumonia characterizedby clinical symptoms and signs (e.g., cough,fever, lung infiltration observed on a chest radiograph) similarto those of pneumonias resulting from other pathogens.LD is caused by infection with Legionella spp. bacteria,which are most often transmitted to persons through inhalationof bacteria disseminated into the air as an aerosol fromnatural or man-made sources of water (1). The incubationperiod is 2–14 days. LD is thought to account for 2%–20%of all community-acquired pneumonias (2) and is fatal in≈6%–11% of cases (3,4).After a large outbreak of LD at a flower show inBovenkarspel, the Netherlands, in 1999 (5), preventionand control of Legionella spp. infections became a nationalconcern in the Netherlands, and legislation to prevent Legionellaspp. in drinking water systems was introduced (6,7).This legislation obligated owners of aerosol-producing devices(e.g., shower heads and whirlpools), if third partiesAuthor affiliations: Regional Public Health Laboratory Kennemerland,Haarlem, the Netherlands (J.W. Den Boer, S.M. Euser, L. Reijnen,J.P. Bruin); National Institute for Public Health and the Environment,Bilthoven, the Netherlands (P. Brandsema)DOI: http://dx.doi.org/10.3201/eid2107.141130may be exposed to them, to conduct a risk analysis, developa control plan, keep logs of control measures, and performregular sampling for Legionella spp. contamination. In addition,in 2002, a National Legionella Outbreak DetectionProgram (NLODP) was implemented (8) on the basis of areport that LD outbreaks are often preceded and followedby small clusters of solitary cases (9). The aims of NLODPare early detection of small clusters of cases, identificationof sources of infection, and implementation of early controlmeasures to prevent additional LD cases or an outbreak.For evaluation of transmission pathways, infection sourcesare sampled, and genotypes of Legionella strains found inthese samples are compared with those of clinical isolate(s)from the patient(s) associated with that source. To evaluatethe findings of the NLODP during 2002–2012, we analyzeddata to determine whether extensive investigation effortscould detect Legionella spp. in collected samples and conclusivelyidentify environmental sources.MethodsPatientsLD has been notifiable in the Netherlands since 1987. Acase of LD is defined as laboratory-confirmed infection ina person having symptoms compatible with pneumonia orradiologic signs of infiltration. Laboratory evidence maybe >1 of the following: isolation of Legionella spp. fromrespiratory secretions or lung tissue, detection of L. pneumophilaantigen in urine, seroconversion or a >4-fold risein antibody titers to L. pneumophila in paired acute- andconvalescent-phase serum samples, a high antibody titer toL. pneumophila in a single serum sample, and direct fluorescentantibody staining of the organism or detection ofLegionella DNA by PCR in respiratory secretions or lungtissue. In the Netherlands, microbiologic laboratories involvedin the diagnosis and treatment of patients with pneumoniaare requested to send available clinical isolates ofLegionella spp. to the Legionella Source Identification Unit(LSIU), a part of the NLODP. LD cases in persons who hadbeen outside the country for >5 of 9 days before disease onsetwere defined as nondomestic cases and excluded fromEmerging Infectious Diseases • www.cdc.gov/eid • Vol. 21, No. 7, July 2015 1167