After a Thanksgiving meal at a San Francisco Bay Area- American Legion Hall left three people dead and over two dozen others ill, health officials have now identified the cause— Clostridium perfringens bacteria.

"Clostridium perfringens is one of the most common foodborne illnesses in the U.S," said Dr. Louise McNitt, deputy health officer for Contra Costa Health Services, according to KTVU. "It can be found in the human intestine without hurting us, but eating food containing large amounts of this bacteria can cause illness and, in some cases, death."

According to KTVU, some of the food for the over 800 attendees was prepared and brought from homes, some food was donated by stores or restaruants and some of the meal was prepared at the Legion Hall.

It’s not clear which dish caused the illness, but analysis from the Centers for Disease Control and Prevention (CDC) confirmed the presence of Clostridium perfringens in the stool of those sickened by the meal. Tests from the reported cases came back negative for 21 foodborne diseases, including salmonella and E. coli.

"Our investigation was not able to determine exactly what people ate that made them sick," said Dr. Marilyn Underwood, CCHS Environmental Health director, according to KTVU. "But after extensive interviews, we found most of the ill people ate turkey and mashed potatoes and they all ate around the same time. Some dishes served at the event, including cooked turkey, were brought to the site after they were prepared in private homes."

Three people died after attending the event and the health department reported 25 incidents of foodborne illness from victims ranging in age from teenagers to people in their 70s.