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Legionella Outbreak Detection, the NetherlandsTable 5. Cluster locations reported for 266 Legionnaires’ disease patients, the Netherlands, 2002–2012*Cluster type, no. (%)Reported cluster locationNo. (%) clustersLocation†Geographic‡Garden center 27 (25.7) 27 (27.6) 0Hospital/health care setting 17 (16.2) 17 (17.3) 0Residence 10 (9.5) 4 (4.1) 6 (85.7)Wellness center§ 9 (8.6) 9 (9.2) 0Hotel 7 (6.7) 7 (7.1) 0Cooling tower 5 (4.8) 5 (5.1) 0Holiday park 5 (4.8) 5 (5.1) 0Swimming pool 4 (3.8) 4 (4.1) 0Industrial complex 3 (2.9) 2 (2.0) 1 (14.3)Car wash installation 3 (2.9) 3 (3.0) 0Sports facility 2 (1.9) 2 (2.0) 0Cruise ship 2 (1.9) 2 (2.0) 0Other 11 (10.5) 11 (11.2) 0Total 105 (100.0) 98 (100.0) 7 (100.0)*Study period was August 1, 2002–August 1, 2012.†A location cluster is defined as cases reported within 2 years of each other in >2 persons who were reported to have been exposed to the same potentialsource of infection during the 2–14 days before symptom onset.‡A geographic cluster is defined as cases in >3 persons who lived 40% of those investigations were positive for Legionellaspp. This well-known source of LD outbreaks should beconsidered often during source identification and investigationefforts performed by the MHS and LSIU.For each patient, a mean of 1.5 potential sources ofinfection were reported, and about half of the reportedsources were sampled. Although several attributes arebeing used by the MHS to improve source investigation (e.g.,an elaborate questionnaire and a geographic informationsystem implemented in 2009 [https://lpgis.geoxplore.nl/webify/?app=lpgis_ggd]), the number of sources beingsampled could be increased. When the genotypic matcheswere analyzed, the mean number of sources identified andinvestigated for the patients involved was considerablyhigher (1.9 sources per patient), suggesting that identificationand investigation of more potential sources ofinfection by the MHS may increase the proportion of patientswith LD for whom a likely source of infection canbe established.Garden centers ranked third (after residences and workplaces)on the list of the most frequently reported potentialsources of LD infection; 26% of identified clusters were associatedwith a garden center, indicating that this source typeis often visited by patients with LD during the 2–14 daysbefore symptom onset. However, only 8 of 86 investigatedgarden centers were found positive for Legionella spp. duringsource investigations. Several studies have shown theTable 6. Genotypic matches (n = 38) from available isolates (n = 41) by source type reported for patients with Legionnaires’ disease,the Netherlands, 2002–2012*Source type No. (%) matches No. (%) available isolatesHospital/health care setting 15 (39.5) 17 (41.5)Residence 7 (18.4) 8 (19.5)Industrial complex 3 (7.9) 3 (7.3)Swimming pool 2 (5.3) 2 (4.9)Wellness center† 3 (7.9) 3 (7.3)Hotel 2 (5.3) 2 (4.9)Travel trailer 1 (2.6) 1 (2.4)Whirlpool 2 (5.3) 2 (4.9)Sports facility‡ 1 (2.6) 1 (2.4)Potting soil 1 (2.6) 1 (2.4)Car wash installation 1 (2.6) 1 (2.4)Total 38 (100.0) 41 (100.0)*Study period was August 1, 2002–August 1, 2012. Data from the LD outbreak in Amsterdam in 2006 (7) are excluded from these data.†Recreational facility offering spas, saunas, fitness equipment, massages, etc.‡This genotypic match was made with a clinical isolate collected during 2000 and an environmental strain collected in 2005.Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 21, No. 7, July 2015 1171