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Aims: For the majority of sporadic Legionnaires' disease cases the source of infection remains unknown. Infection may possible result from exposure to Legionella bacteria in sources that are not yet considered in outbreak investigations. Therefore, potential sources of pathogenic Legionella bacteria-natural soil and rainwater puddles on roads-were studied in 2012. Methods and Results: Legionella bacteria were detected in 30% (6/20) of soils and 3·9% (3/77) of rainwater puddles by amoebal coculture. Legionella pneumophila was isolated from two out of six Legionella positive soil samples and two out of three Legionella positive rainwater samples. Several other species were found including the pathogenic Leg. gormanii and Leg. longbeachae. Sequence types (ST) could be assigned to two Leg. pneumophila strains isolated from soil, ST710 and ST477, and one strain isolated from rainwater, ST1064. These sequence types were previously associated with Legionnaires' disease patients. Conclusions: Rainwater and soil may be alternative sources for Legionella. Significance and Impact of the Study: The detection of clinically relevant strains indicates that rainwater and soil are potential sources of Legionella bacteria and future research should assess the public health implication of the presence of Leg. pneumophila in rainwater puddles and natural soil.

In the Netherlands, rainwater becomes more and more popular as an economic and environmentally sustainable water source for splash parks, however, the associated public health risk and underlying risk factors are unknown. Since splash parks have been associated with outbreaks of infectious diseases, a quantitative microbial risk assessment was performed using Legionella pneumophila as a target pathogen to quantify the risk of infection for exposure due to inhalation and Campylobacter jejuni for ingestion. Data for L . pneumophila and C. jejuni concentrations in rainfall generated surface runoff from streets were extracted from literature. Data for exposure were obtained by observing 604 people at splash parks, of whom 259 were children. Exposure volumes were estimated using data from literature to determine the volume of exposure through inhalation at 0.394 μL/min (95% CI-range 0.0446–1.27 μL/min), hand-to-mouth contact at 22.6 μL/min, (95% CI-range 2.02 –81.0 μL/min), ingestion of water droplets at 94.4 μL/min (95% CI-range 5.1–279 μL/min) and ingestion of mouthfuls of water at 21.5·10 3 μL/min (95% CI-range 1.17 ·10 3 –67.0·10 3 μL/min). The corresponding risk of infection for the mean exposure duration of 3.5 min was 9.3·10 −5 (95% CI-range 0–2.4·10 −4 ) for inhalation of L. pneumophila and 3.6·10 −2 (95% CI-range 0–5.3·10 −1 ) for ingestion of C. jejuni . This study provided a methodology to quantify exposure volumes using observations on site. We estimated that using rainwater as source water for splash parks may pose a health risk, however, further detailed quantitative microbial analysis is required to confirm this finding. Furthermore we give insight into the effect of water quality standards, which may limit infection risks from exposure at splash parks.