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Tuesday, November 29, 2022

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SDSU Study Detects Harmful Viruses in Local Coastal Waters

By Gina Speciale

As a potentially wet El Nino winter looms on the horizon, new research from San Diego State University shows the health dangers from contaminated coastal waters after rain go beyond bacterial infections.

A new study by SDSU public health professor Rick Gersberg shows that after rainfall, coastal waters near the U.S.-Mexico border almost always harbor harmful viruses, in addition to the bacteria that are usually measured to detect health threats.  The study is published in this month’s issue of Applied and Environmental Microbiology.

“It’s important to recognize the presence of the viruses, because it’s the viruses that actually pose the most significant public health risk, and viruses can be present long after the bacteria levels have subsided,” said Gersberg, head of the Division of Occupational and Environmental Health in SDSU’s Graduate School of Public Health.

The study examined a total of 20 water samples taken between 2003 and 2005 at two sites: the surf zone at the mouth of the Tijuana River, and the surf zone near the Imperial Beach pier.  Samples were taken in both wet and dry weather conditions.  The goal was to quantify the levels of hepatitis A viral particles and other indicators of fecal pollution in the vicinity of the U.S.-Mexico border. 

“These locations were chosen because the mouth of the Tijuana River is the single largest source of pathogens to this area of ocean, and Imperial Beach is where the greatest amount of swimming and surfing is done in this area,” Gersberg said.  “Until now, relatively little was known regarding the levels of human enteric viruses in this region.”

Fourteen samples were taken immediately after a rain event of more than 0.5 centimeters or more in a 72-hour period during the wet season of late October through April.  At Imperial Beach, HAV and enteroviruses were detected 79 and 93 percent of the time, respectively.  At the Tijuana River mouth, HAV was detected 86 percent of the time, and enteroviruses  were found in 100 percent of the samples.

Gersberg’s study is the first quantitative assessment of the statistical relationship between levels of hepatitis A, enterovirus, E. coli and enterococci in marine waters.

Gersberg said the high levels of hepatitis A viruses measured during wet weather in San Diego can be attributed to the inadequate sewage collection infrastructure in that region.

During the wet season swimming in these locations is highly unadvisable within 72 hours after a rain event, Gersberg said. 

“Swimmers and surfers could experience anything from stomach cramping to a serious viral infection if they come in direct contact to this level of pollution,” Gersberg said.  “It is also possible to contract the hepatitis A virus if the polluted water is ingested.”

The good news, Gersberg said, is that there appears to be little risk from viruses during dry periods.  During the dry season of May through early October, six samples were collected at the Imperial Beach location.  In all samples, the concentrations of the viruses were below the limit of detection.  (Samples were not taken from the mouth of the Tijuana River during the dry period, because the flow of the Tijuana River at this time is negligible or even zero.) 

“What this shows us is that the levels of bacteria and viruses during the rainy season don’t persist during the dry season,” Gersberg said.  “So health-wise, it’s perfectly safe for swimmers and surfers to be in the water in these locations when we do not have any rain.” 

The Graduate School of Public Health (GSPH) at SDSU is one of four nationally accredited schools of public health in California.  It was founded in 1980 as part of the university's new focus on health and human services. The GSPH provides both undergraduate and graduate education in population-based health disciplines to prepare students for professional health and public health careers, and to enhance the knowledge and abilities of current health professionals.