Same-day Enterococcus qPCR results of recreational water quality at two Toronto beaches provide added public health protection and reduced beach days lost

Abstract

ObjectivesWe evaluated the potential impacts from using a rapid same-day quantitative polymerase chain reaction (qPCR) monitoring method for beach posting outcomes at two Toronto beaches.MethodsIn total, 228 water samples were collected at Marie Curtis Park East and Sunnyside Beaches over the 2021 summer season. Water samples were processed using the USEPA 1609.1 Enterococcus qPCR-based method. Escherichia coli (E. coli) culture data and daily beach posting decisions were obtained from Toronto Public Health.ResultsNo significant correlation was observed between previous-day and same-day (retrospective) E. coli enumeration results at any Sunnyside Beach transect, and only relatively low (R = 0.41–0.56) or no significant correlation was observed at sampling transects for Marie Curtis Park East Beach. Comparing our same-day Enterococcus qPCR data to Toronto’s 2-day E. coli geometric mean beach posting decisions, we noted the need for additional postings for 1 (2%) and 3 (8%) missed health-risk days at Sunnyside and Marie Curtis Park East Beaches, respectively. The qPCR data also pointed to incorrect postings for 12 (31%) and 6 (16%) lost beach days at Sunnyside and Marie Curtis Park East Beaches, respectively.ConclusionApplication of a rapid Enterococcus qPCR method at two Toronto beaches revealed 5% of beach posting decisions were false negatives that missed health-risk days, while 23% of decisions were false positives resulting in lost beach days. Deployment of the rapid same-day qPCR method offers the potential to reduce both health risks and unnecessary beach postings.