Monitoring <i>Legionella</i> in Drinking Water: Should We Focus on <i>L. pneumophila</i> or All Species to Effectively Protect Public Health?

<i>Legionella pneumophila</i> is responsible for the majority of reported Legionnaires' disease cases worldwide. However, environmental monitoring of building plumbing systems often targets a broad range of <i>Legionella</i> species, raising the question of whether monitoring should focus exclusively on <i>L. pneumophila</i> or include all <i>Legionella</i> species. This review examines the policy and public health implications of both strategies by assessing case attribution data for Legionnaires' disease, the environmental prevalence of <i>Legionella</i> species, and the validity of using non-<i>pneumophila</i> counts as indicators for <i>L. pneumophila</i>. Although over 30 species can cause illness, <i>L. pneumophila</i> dominates culture-confirmed cases despite the frequent detection of <i>L.</i> non-<i>pneumophila</i> species in building plumbing and other known sources. Ecological differences between species, including growth temperatures and disinfection resistance, arguably limit the suitability of <i>L.</i> non-<i>pneumophila</i> species as reliable indicators for <i>L. pneumophila</i>. As a result, using all <i>Legionella</i> species counts to inform risk management may lead to excessive interventions without proportional public health benefits. We conclude that routine monitoring should prioritize <i>L. pneumophila</i> to ensure targeted, cost-effective, and health-relevant risk management. Broader monitoring may be warranted in high-risk settings or where local epidemiological data justify a more inclusive approach. These findings support risk-based regulatory frameworks that align monitoring targets with public health outcomes.