Discrete Storm Impacts on the Loading of Salmonella In a Rural Watershed

Normally associated with food, Salmonella and campylobacters both are also among the top waterborne diseases that cause gastroenteritis. In the Little River, a positive relationship between increased environmental pathogen levels and rainfall has been previously demonstrated, consistent with other watershed studies. In this study, we investigated the impacts that individual storm events had on microbial loading of pathogens in the Little River Watershed. We hypothesized that contamination in this watershed would be higher during storm events when compared against the baseline samples. Between January and December 2007, 5 storm samples and 5 baseline water samples were collected from three stations within the LRW. Storm samples were collected when at least 1.3 cm (one-half inch) of consistent rain had fallen over the watershed. Baseline samples were collected during periods when no rain had fallen for at least seven days prior to sampling. During this study, one-hundred one Salmonella isolates, representing sixteen S. enterica subsp. enterica serotypes, and one-hundred eighty nine campylobacter isolates were recovered and identified, including six Salmonella serotypes commonly isolated from humans in Health District 8-1 during 2007 (S. Bareilly, S. Java, S. Muenchen, S. Montevideo, S. Rubislaw, and S. Typhimurium). Significantly higher Salmonella and campylobacter levels were consistently detected in storm samples compared against baseline samples (p = 0.007 and p < 0.001, respectively). Individual monthly Salmonella levels ranged from non-detectable (< 1.8 MPN L^-1) to a high of 350 MPN L^-1, recovered from Site 03 during a June storm sample. Storm samples also reflected significantly higher Salmonella serotype diversity compared to baseline samples (p = 0.006). Campylobacter levels ranged from non-detectable (< 5 CFU ml^-1) to approximately 15,700 CFU ml^-1, collected during a July storm sample from site 03. Given the high pathogen levels observed after storm events and finding clinically relevant Salmonella strains in the environment, ambient waters may be an underappreciated source of Salmonella or campylobacter exposure.