Risk of gastrointestinal illness due to Campylobacter exposure in urban waterways for unsheltered persons experiencing homelessness.

As the population of persons experiencing homelessness (PEHs) continues to grow in urban areas, including Las Vegas in Southern Nevada, it becomes increasingly important to quantify and mitigate health risks encountered by this vulnerable population. This study examines exposure risks from Campylobacter, a leading cause of bacterial gastroenteritis, among unsheltered PEHs who utilize untreated water from Las Vegas' flood control tunnels and washes for personal hygiene and cleaning. Utilizing quantitative microbial risk assessment (QMRA), we evaluated three exposure scenarios: direct bathing, toothbrushing, and hand-to-mouth contact following hand submersion. The median probability of illness for a single toothbrushing (5 %) or bathing event (5 %) exceeded the adopted risk threshold of 3.2 %, with estimated median annual risks reaching 36 % under monthly exposure frequencies. High concentrations of Campylobacter in these urban waterways underscore the urgent need for targeted interventions, including improved access to clean water and sanitation facilities, to mitigate the health risks faced by PEHs. This study provides a step forward in understanding and addressing the risks of interacting with water in urban waterways, including flood control infrastructure.