Application of Same-Day Enterococcus qPCR-Based Analyses for Quality Assessment of Shorelines (Water and Sand) at Recreational Beaches

Rapid water-quality monitoring methods for beach water and sand can be helpful for public health authorities to develop comprehensive beach monitoring programs. In this study, we evaluated the performance of the Enterococcus qPCR (USEPA 1609.1) method for quality monitoring of beach water and sand-porewater at two Niagara region beaches in Ontario, Canada (Lakeside and Sunset Beaches). While the USEPA 1609.1 method has been validated for beach water, its potential for assessing associated beach sands (which may function as a microbial reservoir) has not been fully explored. All beach water samples (n = 168) passed the qPCR quality control (QC). However, only 20 out of 48 (41.7%) sand-porewater samples passed the qPCR QC, potentially due to interference by soluble inhibitors. The proportion of the sand-porewater samples passing QC improved slightly to 63 out of 120 (52.5%) with a prefiltration step to remove sand and other large particles. The faecal indicator density in the sand-porewater, tested in parallel, did not correlate with the beach water faecal indicator density. Comparing beach water data for the same-day Enterococcus qPCR threshold with the previous-day E. coli culturing-based threshold across all beach days tested, Enterococcus qPCR analyses identified 3 (7%) and 7 (16%) false positive/lost beach days for Lakeside and Sunset Beaches, respectively. Additionally, of the total beach days tested, Enterococcus qPCR analyses identified 2 (5%) and 1 (2%) false negative/health-risk days for Lakeside and Sunset Beaches, respectively. Sand-porewater testing analyses identified days when faecal indicators (in the sand) exceeded beach water quality thresholds. Compared with conventional E. coli culturing, use of the same-day qPCR method would result in fewer beach postings and could identify several additional health-risk days (when the beaches may not be posted). Future studies could include additional prefiltration steps or modifications in the Enterococcus qPCR protocol to improve the method's applicability for sand quality monitoring.