Assessment of Legionella pneumophila in Rural Homes Supplied by Private Well Water

Legionella pneumophila is a major cause of waterborne disease in the United States, but little is known about its prevalence in rural homes supplied by domestic well water. With a citizen science campaign involving 57 such homes in Illinois, conclusive results from 39 homes showed intact L. pneumophila in 31% and 28% of warm and hot water samples, respectively. We conducted a quantitative microbial risk assessment (QMRA) for L. pneumophila infection risk using L. pneumophila data from three studies (ours, another on rural homes in North Carolina, and another on a public water supply). The risk of illness was non-negligible in all cases and sometimes exceeded the 10^-4 target annual risk. The L. pneumophila concentration and exposure time had the greatest impact on the risk of illness due to a one-time exposure. Aerosol concentration had the greatest impact on the annual risk of illness. A maximum L. pneumophila concentration of 6 × 10^-3 copies/mL was needed to achieve the 10^-4 target. This study showed that L. pneumophila risk could be present in homes supplied by private wells, like those studied here, but can be mitigated by reducing L. pneumophila concentration, reducing exposure time, and careful consideration of fixtures that produce high concentrations of respirable aerosols.