Lognormal distributions capture site-specific variability in enteric virus concentrations in wastewater

As more data on virus concentrations in influent water from wastewater treatment plants (WWTPs) becomes available, establishing best practices for virus measurements, monitoring, and statistical modelling can improve the understanding of virus concentration distributions in wastewater. To support this, we assessed the temporal variability of norovirus, adenovirus, enterovirus, and rotavirus concentrations in influent water across multiple WWTPs in Switzerland, the USA, and Japan. Our findings demonstrate that the lognormal distribution accurately predicts temporal variations in concentrations for all viruses at all sites, outperforming the gamma and Weibull distributions that do not capture high variability. However, important differences in variability and uncertainty were observed across systems, underscoring the need for site-specific assessments. Using lognormal parameters, we identified optimal monitoring frequencies to balance cost-effectiveness and precision. For most sites, weekly monitoring would be sufficient to estimate the annual average concentration of enteric viruses within a 95% confidence interval of 0.5-log10. We examined the mechanistic basis of the lognormal distribution, highlighting processes that drive its prevalence and shape the behavior of its upper tail. By integrating these insights, this study provides a novel statistical foundation for optimizing virus monitoring frameworks and informing public health interventions targeting wastewater systems.