County Reveals DNA-Based Ocean Water Testing System For Quicker Results

By Elizabeth Ireland, Times of San Diego

May 5, 2022

San Diego County began using a DNA-based ocean-water testing technology Wednesday, intended to produce faster results and earlier warnings when bacteria reach unhealthy levels along the county’s coast.

County employees and elected officials gathered in Imperial Beach Wednesday morning to unveil the technology.

County Board of Supervisors Vice Chair Nora Vargas said the county plans to expand its use of the droplet-digital polymerase chain reaction testing technology to more than 70 miles of shoreline the county samples and tests to protect the public.

“I’m happy to announce with today’s sampling, San Diego becomes the first coastal county in the nation to implement the ddPCR method for beach water sampling,” she said. “Faster results are going to allow the county to issue or lift beach advisories on the same day samples were collected. And it reduces the time the public could unknowingly be at risk and when the water is contaminated.”

The new system will let the county sample beach water in the morning, get results and warn the public by the afternoon instead of the next day.

Imperial Beach’s waters often suffer from high bacteria levels largely due to sewage runoff from neighboring Tijuana and water contact closures are routinely issued. The problem sometimes extends up Silver Strand toward Coronado.

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. The county’s Public Health laboratory and the state conducted a side-by-side study of how the DNA testing compared to the petri dish system in 2019.

In February, the California Department of Public Health gave the new system its final laboratory approval.

City News Service contributed to this article.

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