( CNN ) -- The investigation of the E. coli outbreak linked to Nestle Toll House cookie dough is nearly over , according to the U.S. Food and Drug Administration . The cause of the contamination has not been identified . Nestle recalled all its Toll House refrigerated cookie dough products made at a Danville , Virginia , plant . David Acheson , the FDA 's associate commissioner for foods , says the samples of cookie dough his agency has tested do not contain the E. coli strain that sickened 74 people in 32 states . On June 19 , Nestle recalled all its Toll House refrigerated cookie dough products made at a Danville , Virginia , plant . Thirty-four people have been hospitalized ; no deaths have been reported . The CDC reports that the majority of the patients were teenage girls who reported eating the cookie dough raw . Last month , the FDA found E. coli in a production sample of Toll House cookie dough , but after testing , investigators found that the strain in the sample did not match the outbreak strain . `` We are still in speculation mode , '' Acheson said , but the E. coli `` most likely came from raw ingredients '' such as flour . The E.coli strain that caused the outbreak , 0157 : H7 , is typically found in fecal contamination from animals such as cows , sheep or goats . Acheson points out that it 's not unusual for those animals to be carrying more than one strain of the bacteria . But he believes that the root cause of the contamination may never be known . `` We have to conclude we 're unlikely to have a definitive determination , '' he said . Most people with E. coli 0157 : H7 experience diarrhea and abdominal cramps within eight days of infection . The FDA notified Nestle USA on Thursday that its investigation at the Danville plant was over . Nestle says FDA inspectors were at the plant for more than a week and found no E. coli on equipment . More than 1,000 tests have been conducted at the facility after the outbreak . `` We 've dismantled the production line and done extensive testing on all equipment and not found any E. coli , '' Nestle USA spokeswoman Laurie MacDonald said . MacDonald announced that Nestle is easing back into production at the plant . The company has purchased new lots of eggs , flour and margarine and says it is thoroughly testing the new products and all raw ingredients . Consumers will have to wait to see cookie dough back in grocery stores . `` You 're not going to see anything on the shelves for quite some time , '' MacDonald said . But when it does appear , the company will mark the cookie dough with a new label that clearly designates it as a new batch . It will also continue to carry a reminder to not eat the dough raw .
FDA says Toll House samples do n't contain particular strain of E. coli . Nestle recalled all dough made at Virginia plant after outbreak . 74 people in 32 states were sickened ; there were no deaths . Plant resuming test production of cookie dough .