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Researchers Probe Dangers in Urban Runoff

09/20/99
Scientists on both campuses look at the presence of disease-causing organisms found near storm drains; a beach that seems pristine may not be.
by Bob Calverley
Marine biologists Jed Fuhrman and Rachel Noble, in their Wrigley Institute lab, show how ocean water is tested for viruses using a water filtration system.

Photo by Irene Fertik
Two separate research efforts at USC are shining an ever-brightening light on a murky problem at the beach – the presence of disease-causing organisms, particularly pathogenic viruses, in untreated urban runoff.

For the past five years, marine biologists Jed Fuhrman and Rachel Noble have been searching the coastal waterways of Southern California for viruses.

They’ve found that pristine beaches near storm drains often demonstrate the presence of human enteric viruses, a viral family inhabiting sewage that can cause intestinal illness. Focusing on the enterovirus group, including poliovirus and cocksackie virus, they have also detected hepatitis A virus in a few samples.

FUHRMAN AND NOBLE’S research is partly funded through the National Oceanic and Atmospheric Administration’s Sea Grant program.

Meanwhile, Robert Haile, professor and director of the genetic epidemiology program in the Keck School of Medicine of USC, has published the first large-scale study to tie adverse health effects to swimming near storm drains where urban runoff from Los Angeles enters Santa Monica Bay.

Published in the July issue of Epidemiology, Haile’s study was conducted in the summer of 1995 at Santa Monica, Will Rogers and Surfrider beaches. His team interviewed 10,459 swimmers and conducted bacterial analyses of water on the days they went swimming. Nine to 14 days later, the researchers re-interviewed the swimmers by telephone to see if they had been sick. The project also included virus tests in storm drains themselves.

THE RESEARCHERS found positive associations between a broad range of gastrointestinal, upper respiratory and other health problems and distance from the drain, bacterial indicators and presence of enteric viruses. The number of new health problems attributable to the swimmers’ exposure reached well into the hundreds per 10,000 exposed subjects.

“This finding implies that these risks might not be trivial when we consider the millions of persons who visit these beaches each year,” the study said.

The standard for determining water quality at beaches is to test for coliform bacteria, denizens of sewage. The tests are quick, simple and inexpensive, but evidence is growing that the bacteria tests may not be enough.

“We’re finding that the presence of virus doesn’t correlate very well with bacterial measurements,” said Fuhrman, who holds the McCulloch-Crosby Chair in Marine Biology in the College of Letters, Arts and Sciences. “Just because tests don’t find a dangerous level of bacteria doesn’t mean there aren’t viruses out there that can make you sick.”

Fuhrman, who authored a comprehensive review article on viruses in the June 10 issue of Nature, said there is no reason why viruses and bacteria should always be together.

“Bacteria live and they die, they feed and they reproduce,” he said. “Viruses are much smaller – just a piece of genetic material surrounded by a coat, and they have no metabolism. They react differently with the environment.”

Haile reported in his paper that viruses “die off at slower rates in sea water than do bacteria, and they can cause infection at a much lower dose.”

Governments are not likely to begin routine testing for viruses at beaches soon. Fuhrman estimates the virus tests that he and Noble adapted to fit their materials and equipment cost roughly $1,000 each.

Noble, a postdoctoral scientist at the Wrigley Institute for Environmental Studies and the Southern California Coastal Water Re search Project, said that for each test she collects a 20-liter sample of sea water. She then uses a series of filtering and concentration procedures to end up with about one-fiftieth of a drop that may contain viruses. The scientists employ a process called reverse transcriptase polymerase chain reaction to make a DNA copy of the RNA present in viruses.

“We have to amplify that DNA until it is detectable,” Fuhrman said. “And we have to know the gene sequences of the viruses that we are looking for. We know many of the enteroviruses, so we usually look for them. I’m sure there are a lot of viruses out there that we aren’t testing for, and probably many more that we could look for if we wanted to and had the resources – cold viruses, for example.”

Noble said it takes 18 to 20 hours to perform a single test.

After performing 80 such tests at beaches, Fuhrman and Noble believe the evidence is strengthening that viruses from urban runoff pose a significant health problem.

Haile said that “the debate has shifted from whether there was a risk to agreement that there is a risk, and now to, what should we do about it?”

Fuhrman, who often takes his children to the beach, said he would continue to do so. He noted that the ocean is not a laboratory and that most of the time most beaches are safe.

Noble added that their tests have mainly found viruses only near storm drains. “Places like Manhattan Beach or Zuma Beach where there aren’t storm drains appear to be in pretty good shape,” she said.

Fuhrman said beachgoers need to be more aware that the urban runoff entering the ocean from storm drains can make them sick.

“I’ve seen people bathing right next to a warning sign. I’ve seen parents rinsing the sand off their kids with storm-drain water,” he said. “They wouldn’t do that if they knew where storm-drain water came from.”