Even with the clearance, investigators have not been able to pinpoint the original source of contamination. Designed by Freepik, www.freepik.com

 

CHICO, CA (MPG) - County health officials say the source of the toxic E. coli strain that sickened five people over the summer has still not been identified, despite months of testing along Big Chico Creek and extensive investigation by local, state and federal agencies.

The June outbreak involved a dangerous Shiga toxin-producing strain of E. coli that likely came into contact with swimmers. 

Dr. Jarett Beaudoin, Butte County’s Public Health Officer, told the Board of Supervisors during a Dec. 16 presentation that the infections were linked to water and sediment in Big Chico Creek, including areas around Sycamore Pool and as far as five miles upstream.

“E. coli is a very common bacteria, but this is a particularly toxic variant,” Beaudoin said. “It landed three children in the hospital and two on dialysis. It is very serious for us.”

The county issued a no swim advisory in June and began working with the California Water Board and state health authorities to conduct repeated testing. Retesting in October showed no presence of the outbreak strain, and the advisory was lifted on Oct. 21.

Even with the clearance, investigators have not been able to pinpoint the original source of contamination. The leading hypothesis from the Centers for Disease Control and Prevention, the California Department of Public Health and county investigators points to cattle or other ruminants, such as goats and sheep. Tests on geese and deer near the creek were negative, Beaudoin said. 

Although not a current theory, sediment movement from burn scar areas, including land affected by the Park Fire, may have contributed to the spread or persistence of bacteria during the summer. 

“It is something we want to keep watching for, and we are,” Beaudoin said. “If we get a case of this type of E. coli, we’re probably going to do aggressive monitoring.” 

There are no immediate plans for additional source‑tracking work. Public Health will continue monitoring for human cases next season and is coordinating with the California Water Board and the City of Chico on preventive water testing. Any new cases of the same strain would trigger an immediate no swim advisory, Beaudoin said. 

With winter rain, Beaudoin said there is concern that runoff could reintroduce contamination. However, similar outbreaks in past years have not returned the following season, suggesting the bacteria does not persist long‑term in creek sediment, he said. 

All five individuals affected in June are reported to be doing well with no known lasting complications.