June 30, 2006
How’s the Water?
Is it safe to swim at the local beach? Answering that question is the job of public officials who routinely monitor levels of fecal indicator bacteria at swimming beaches. The water quality tests they use, however, take about 24 hours to process. As a result, contaminated beaches may remain open when they should be closed, and safe beaches may be closed after the threat has washed away.
A recent study, conducted by the Southern California Coastal Water Research Project (SCCWRP) with support from CICEET, compared new, rapid microbial testing methods that have the potential to make same-day health risk warnings possible. The results have been published in a report, "Evaluation of Rapid Microbiological Methods for Measuring Recreational Water Quality," now available online.
The study examined six approaches to rapid microbial indicator detection: three quantitative polymerase chain reaction (QPCR) methods that tag microbial DNA with a fluorescent probe; transcription-mediated amplification (TMA), which uses fluorescent tagging to quantify RNA; dual wavelength fluorimetry (DWF), which combines fluorescent substrates with advanced optical detection; and an immunological “dipstick,” designed to determine whether bacterial concentrations exceed California’s single-sample standard. Although the study focused primarily on enterococci, two of the six research groups involved also measured E. coli.
Results from two QPCR approaches and the TMA method demonstrated more than 80 percent accuracy with respect to the State’s standards for enterococci testing. Results for one of the E. coli QPCR methods were even more promising, displaying 90 percent agreement with beach management decisions based on standard testing methods.
Based on this data, California’s Beach Water Quality Workgroup has determined that the QPCR and TMA methods appear ready for use. This year, a round of beta testing will confirm the accuracy of these results and the practicality of these technologies for use by local water quality laboratories. The Orange County Sanitation District and County of Orange Public Health Laboratories have agreed to participate in the study as beta testing facilities.
"Evaluation of Rapid Microbiological Methods for Measuring Recreational Water Quality" is available by PDF. Or, you can download a specific section of the report.