Sun and sand worshippers should heed contamination warnings posted along beaches, especially near the U.S.-Mexico border, research showed.

A two-year study by San Diego State University professor Rick Gersberg confirmed the validity of contamination warnings posted at the mouth of the Tijuana River and in Imperial Beach, the San Diego Union-Tribune said Friday.

Gersberg's study examined water samples taken from 2003 to 2005 at the mouth of the Tijuana River and in the surf zone at Imperial Beach. Samples taken during dry weather confirmed the water was safe. But after rainstorms, Gersberg found Hepatitis A and other viruses at the same beaches where county officials posted warnings.

Gersberg said he wasn't surprised by the findings, considering the source of the contamination is urban runoff from the Tijuana region, where 25 percent to 30 percent of homes and businesses are not connected to a sewer system.

In detecting the water-borne viruses, Gersberg used high-tech genetic testing, which yielded accurate results in hours. Current bacteria-based water testing has been criticized for being slow and prone to false-positive results.

Copyright 2006 by United Press International