PORTLAND, Ore. – Fifty-three individuals were sickened by food tainted with Salmonella, and now it’s up to public health officials with the Multnomah County Health Department to pinpoint what made the conference-goers sick.

Not an easy task considering the department must determine the contamination source from roughly 100 different food dishes served over a four-day period and prepared by multiple caterers. At least 500 individuals attended the event called Open Source Bridge Conference at the Eliot Center in downtown Portland on June 23 to June 26. The illness cluster includes 53 individuals, including nine laboratory confirmed cases.

“We believe this was an isolated event that did not occur beyond the conference,’’ Deputy Health Officer Dr. Jennifer Vines said in a health alert. “We are monitoring illness in Oregon to assure that this is the case.” The department notified other states and the Atlanta-based Centers for Disease Control and Prevention.

The investigation will include collecting surveys from 223 conference participants and laboratory testing of Salmonella from affected individuals. Organizers of the conference are working with the health department to identify individuals who became sick and what they ate in the days before illness onset. Symptoms of Salmonella infection include fever, diarrhea, abdominal pain and/or vomiting.