(AP) -- An extensive investigation has failed to determine how E. coli bacteria was introduced into a northeastern Oklahoma restaurant linked to hundreds of illnesses and one death, the state health board said in a report released Thursday.
The report said analysis suggests there was ongoing foodborne transmission of the bacteria at the Country Cottage restaurant in Locust Grove from Aug. 15 to Aug. 24.
But the report said that since no specimen of the bacteria was found in the restaurant, investigators couldn't determine how it was introduced or spread.
Food samples from the restaurant were examined and showed no signs of contamination, but officials said it was possible the tainted food had already been thrown out.
"What is important to remember is that when responding to an infectious disease outbreak, our primary objective is to rapidly identify the source of the infection to contain the outbreak and prevent any further spread," State Epidemiologist Dr. Kristy Bradley said in a statement.
"Within 48 hours of being notified of increased cases of persons with bloody diarrhea being admitted to Tulsa area hospitals, we identified the Country Cottage restaurant as the common source of transmission. The restaurant closed voluntarily and the outbreak was contained."
According to the report, there were a total of 341 cases of people sickened by the bacteria; 70 were hospitalized and one died. Several young children required dialysis after being sickened.
The Oklahoma Health Department spent 6,481 hours investigating the outbreak, the largest in the nation's history for the rare E. coli strain O111.
The restaurant, which is about 50 miles east of Tulsa, was allowed to reopen after agreeing to a number of conditions including disconnecting a private well on the property, allowing for repeat environmental testing in the restaurant upon request and implementing a monitoring system for employee hand-washing, among others.
Oklahoma Attorney General Drew Edmondson has suggested that tainted well water may have been to blame for the outbreak. He is pursuing a lawsuit against Arkansas poultry companies, alleging that chicken waste has polluted water supplies in the region.
Poultry companies say there's no evidence their industry is responsible for water pollution in the area.
Health inspectors examined a private water well located on the restaurant property, water filters, and the Locust Grove municipal water supply and found no E. coli 0111.
According to the Centers for Disease Control and Prevention, only 10 outbreaks involving E. coli O111 had been reported nationally prior to Oklahoma's outbreak.
©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Explore further: The Ebola outbreak highlights shortcomings in disease surveillance and response – and where we can do better