Home Listing method DNA-Based Water Testing System Launched for San Diego Beaches

DNA-Based Water Testing System Launched for San Diego Beaches


San Diego County has started using new seawater quality testing technology intended to produce faster results and earlier warnings when bacteria reach unhealthy levels.

During the rollout of the DNA-based technology last week, County Board of Supervisors Vice Chairman Nora Vargas said the county plans to expand its use of the testing technology, known as droplet digital polymerase chain reaction, or ddPCR, from more than 70 miles of shoreline that the county is sampling and testing to help protect the public.

“I am happy to announce [that] with today’s sampling, San Diego becomes the first coastal county in the nation to implement the ddPCR method for beach water sampling,” Vargas said at the May 4 launch. “Faster results will allow the county to issue or lift beach advisories on the samples were taken the same day. And it reduces the time the public could be at risk without knowing it and when the water is contaminated.

Officials said the DNA-based system is more sensitive to bacteria levels than the older method, which required growing bacterial cultures from water samples in petri dishes.

“In San Diego, we had 104 advisories in 2021, and about half lasted a day or a little longer, so it’s important that we can test, retest and flag and lift advisories as needed,” Heather Buonomo said. , division director for the county Department of Environmental Health and Quality.

To determine the levels of bacteria in the new system, samples are taken early in the morning and, using the ddPCR method, the DNA is reproduced in the laboratory.

“It’s different from the culture method we used before, where we cultured the bacteria and waited for the incubation period,” Buonomo said. “The new method gives us the information much faster. So we can test at 6 a.m., pick it up at 8 or 9 a.m. so we can have the results the same day. »

Testing sites are chosen based on accessibility for samplers and where there might be a storm drain or runoff containing bacteria. The results apply only to this geographical area.

Getting to this point took a decade.

“It’s been a long time coming. We started thinking about it in 2012,” Buonomo said. “Even then, we were looking for faster ways to deliver information.

“We worked with state health officials and did some testing to see if it would work. Once they had the data, they had to change state law to use this new method. It’s very exciting.”

The information collected is disseminated on sdbeachinfo.com, which provides a list of all active water quality advisories. ◆