Sea Grant Study Says It’s Time to Test Water for More Than Just Bacteria

by Bob Calverley
Jed A. Fuhrman and graduate student Rachel Noble collect seawater samples.

WHEN IS IT SAFE to go in the ocean?

In America and most other countries of the world, the microbiological safety of beaches is determined by testing for the presence of fecal bacteria. Water found to be clear of bacteria is assumed to be safe.

However, a USC Sea Grant study indicates that standard might be misleading because human pathogenic viruses sometimes lurk in bacteria-free water.

“Our results suggest that we should consider performing limited virus testing in recreational waters in the near future, particularly at storm drains adjacent to high-use beaches,” said Jed Fuhrman, holder of the McCulloch-Crosby Chair in Marine Biology. “Viruses are very different from bacteria. While they may come from the same sewage contamination source as bacteria, their subsequent fate in water can be dramatically different.”

Fuhrman and postdoctoral fellow Rachel Noble, who is supported jointly by the USC Wrigley Institute for Environmental Studies and the Southern California Coastal Water Research Project, noted that viruses differ chemically and biologically and are much smaller in size. Under certain conditions, viruses persist longer than bacteria and can be dispersed differently in seawater.

“We found the expected widespread distribution of viruses after heavy rains, but we often found viruses in storm drains, even during the summer dry weather,” said Noble. The viruses detected were usually in the human enteric virus family, which includes poliovirus, echo-virus and Coxsackie virus. Hepatitis A virus has also been detected.

“Viruses probably cause a significant fraction of illnesses associated with sewage-contaminated water,” Fuhrman said. “Our results confirm that it is a wise to avoid swimming near storm drains year round, and even far from the drains after heavy rains.”

FUHRMAN AND NOBLE analyzed water samples from beaches ranging from the Mexico border to Santa Barbara using a state-of-the-art molecular biology test called the Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR), which detects the RNA genetic material of some groups of human pathogenic viruses. The test is a hundred times more sensitive and 10 times faster than virus-culturing methods.

“This is potentially a very good tool for testing beaches because it is fast and would allow decisions to be made quickly,” said Fuhrman. But he added that RT-PCR is so sensitive that it can detect viral genes from inactive viruses, or the presence of viruses at levels so low they do not pose a threat to human health. “It is a valuable indicator to show how viral measurements relate to conventional bacterial indicators.”