Optimal threshold criteria for E. coli qPCR using ROC analyses

Session: 14. - Microbial Dynamics and Human Health Risks in the Beach Sand

Abhilasha Shrestha, University of Illinois at Chicago School of Public Health, [email protected]
Sam Dorevitch, U of Illinois at Chicago School of Public Health, [email protected]

Abstract

USEPA developed a draft qPCR method targeting E. coli for beach monitoring. The fact that new epidemiological data are not concurrently being collected with the development of this method makes it important to identify a health-based E. coli qPCR Beach Action Value (BAV). Health-based BAVs already exist for E. coli culture and enterococci qPCR methods. We sought to identify threshold values for the E. coli qPCR method using existing health-based BAVs.

In 2017, we analyzed 288 water samples from eight Chicago beaches using culture (E. coli) and qPCR (enterococci and E. coli) methods. Water quality exceeded both the enterococci qPCR and E. coli culture BAVs in approximately 18% of the samples. Receiver operating characteristic (ROC) curve analyses were used to define optimized E. coli qPCR BAVs. These BAVs differed from one another, depending on whether the E. coli culture or the enterococci qPCR BAV value was used as the ‘gold standard.’ E. coli culture results from water samples collected, for example, on a Monday, became available on Tuesday. Those results did not predict exceedance of the E. coli qPCR BAV in Tuesday’s water samples. Our findings suggest optimized health-based E. coli qPCR BAVs may be useful for beach monitoring and notification.

1. Keyword
water quality

2. Keyword
Lake Michigan

3. Keyword
environmental policy

4. Additional Keyword
fecal indicator bacteria

5. Additional Keyword
qPCR

6. Additional Keyword
Beach monitoring and management