Paul Fisher/Surfline

The sign means there was dangerous bacteria in the water about 24 hours earlier

About 650 San Diego surfers have volunteered to be lab rats in a study that looks at how closely surfing — particularly during the beach-closure days after rain — correlates with the illnesses they've been warned to stay out of the water to avoid.

"The bacteria — enterococci — we routinely measure do not make you sick," says Ken Schiff, deputy director of the Southern California Coastal Water Research Project. "They are indicators that signal that the pathogens that do may be present."

The study began in 2013, signing up surfers in San Diego and Orange County to answer health questions after participants went surfing and researchers took daily water samples at Tourmaline and the Ocean Beach breaks.

Via the internet or a smartphone app, surfers answered questions about their health since surfing, with some questions focused on ten health problems that include gastro-intestinal distress, sinus and ear problems, skin rashes and infected cuts and scrapes; and respiratory illnesses. If they participated for four weeks, surfers received a gift card to an online surf shop.

During dry weather, the water is pretty clean, Schiff affirmed. But in wet weather, urban runoff and other factors increase the chance of encountering bacteria and pathogens. The question is how to measure them to get results that are relevant to human health.

Schiff said they are trying to determine whether looking for fecal-indicator bacteria including enterococcus — a bacteria found in the gut of warm-blooded animals — is a useful indicator for the presence of viruses (including norovirus and adenovirus) that actually make people sick.

Beach water-quality testing currently looks for fecal-indicator bacteria by culturing it, which means that the most current information is a day old because of the testing method.

"Our current water testing relies on methods that are over 50 years old, where you inoculate a petri dish and stick it in an oven the same temperature as your gut and let it grow for 24 hours," Schiff said. "For the study, we are using technology that lets us take a sample in the morning and have results before noon."

Those results also provide information on the DNA of the bacteria and viruses in the water, and that's important, Schiff says. Not all enterococcus comes from humans, and researchers can identify the source using DNA testing.

"Swimming in dog poop is icky but it likely won't make you sick," he explained.

The coastal project has been doing similar research along the coast for more than a decade, and the results in other places suggest that the presence or absence of enterococci doesn't always correlate to whether or not people get sick.

A coastal project study at Surfrider Beach in Malibu, for example, found an increased risk of gastrointestinal illness when there was little Enterococci presence — an uncommon result, but an important one.

The surfers in the study sound like people you know from the dawn patrol: they surf every three days or more, often at three or fewer breaks, are in the water by 8 a.m. and stay in for an hour or two. The study included surfers who are 79 percent male, 76 percent employed, and they were between 27 and 45 years old, with a median age of 34.

Schiff said learning about the surfers affected how he saw surfing.

"One thing I realized after this study is that many surfers are comparable to any dedicated athlete," he said.

The coastal research project is parsing through its data now and should have conclusions later this year, Schiff said.