Prevalence of private drinking water wells is associated with salmonellosis incidence in Maryland, USA: An ecological analysis using foodborne diseases active surveillance network (FoodNet) data (2007–2016)

Highlights: • Salmonella is a leading cause of bacterial foodborne illness in the US. • Approximately 19% of MD residents rely on private wells as their water source. • Well prevalence is associated with salmonellosis in MD coastal zones. • Agricultural and socioeconomic factors impact salmonellosis in coastal zones. Salmonellosis is a leading cause of foodborne illness worldwide. Salmonella infections have most often been associated with food-related risk factors, including the consumption of eggs and poultry. Recently, socioeconomic, agricultural and environmental factors, including drinking water source, have also been shown to influence the risk of salmonellosis. However, there are few data evaluating the association between consuming private well water and risk of Salmonella infections. Here, we examined the association between the prevalence of private drinking water wells and the incidence of salmonellosis in Maryland. Culture-confirmed salmonellosis case data (2007–2016) were obtained from the Foodborne Diseases Active Surveillance Network. Cases were linked by zip code with data from the Maryland well permits registry, the 2010 U.S. Census, the 2016 American Community Survey, and the USDA Agricultural Census. Well prevalence and salmonellosis incidence rates were calculated by zip code, and associations were evaluated using negative binomial regression models. From 2007 to 2016, a total of 8850 salmonellosis cases were reported in Maryland. Annual incidence rates ranged from 12.98 to 17.25 per 100,000 people. Prevalence of private wells in a zip code was statistically significantly associated with salmonellosis incidence at a statewide level (Incidence Rate Ratio [IRR] = 1.62; 95% Confidence Interval [CI] = 1.35, 1.93) and in the coastal zone of Maryland (IRR = 1.61; 95% CI = 1.31, 1.99). The presence of broiler chicken operations and the percentage of people living below the poverty level were also significantly associated with salmonellosis incidence at the zip code level in the coastal zone. To our knowledge, these are the first U.S. data to characterize the relationship between private drinking water wells and the risk of salmonellosis using an ecological study design. Our findings provide support for Salmonella testing of private wells in Maryland, as well as strengthening private well water regulations and improving the education of homeowners on well maintenance.