Pathogen and indicator trends in southern Nevada wastewater during and after the COVID-19 pandemic

Abstract

Characterization of wastewater concentrations of human enteric pathogens and human fecal indicators provides valuable insights and data for use by regulators and other stakeholders when developing treatment criteria for water reuse applications, performing quantitative microbial risk assessments, or conducting microbial source tracking. Wastewater samples collected over three years during and after the COVID-19 pandemic were analyzed retrospectively (March 2020–September 2022) and prospectively (October 2022–December 2023) by qPCR for molecular markers of adenovirus, enterovirus, norovirus GI & GII, as well as the human fecal indicators pepper mild mottle virus, crAssphage, and HF183 (n = 1112). A sub-campaign was conducted, and wastewater samples were tested for the culturable enteric viruses adenovirus and enterovirus (n = 56) and the protozoan parasites Cryptosporidium and Giardia (n = 73) over one year (January–December 2023). All assays had high detection rates, ranging from 71% to 100%, and were fit to log-normal distributions. All molecular markers for enteric pathogens displayed seasonal and geographic variation, potentially explained by seasonal epidemiology of gastrointestinal illness, differing populations, and differing sample types. Additionally, the impact of Nevada-specific COVID-19 public health guidance (e.g., mask mandates, stay-at-home orders) on enteric pathogen concentrations was characterized, with significantly higher concentrations of molecular markers observed in “non-pandemic” conditions. This study provides high quality (i.e., high sensitivity, minimally censored, recovery adjusted) pathogen and indicator datasets with insights for use in academic, public health/epidemiological, and industry/regulatory applications.