Two more cases of E. coli infection could be linked to strawberries sold at roadside stands and at farmers markets in Oregon, according to the Clatsop County Public Health Department.

The additional suspected cases were reported to the department on Wednesday. At least one of the case patients was said to have eaten strawberries traced to Jaquith Strawberry Farms in Newberg, which has been implicated as the source of the outbreak. 

So far, 15 cases, including one death are tied to the E. coli O157:H7 outbreak, the first in the U.S. attributed to strawberries.

On Thursday the U.S. Food and Drug Administration published the Oregon Public Health safety alert about the strawberries, which advises that strawberries from Jaquith Farms that were frozen or used to make uncooked jam are unsafe and should be thrown out. 

Nearly all the case patients told investigators they had eaten local strawberries before they became ill. Pinpointing the farm was complicated, however, because some vendors had purchased the fruit from Jaquith Farms and then passed it off as their own, according to The Oregonian’s Lynne Terry.

The state agriculture department’s head of food safety told Terry that reselling another farmer’s produce is illegal “but more common than we thought.”

William Keene, senior epidemiologist at Oregon Public Health, suspects deer droppings may have contaminated strawberries in the fields. E. coli  O157:H7 is carried by ruminants, and shed in their excrement.

In 1995, Keene traced an E. coli outbreak associated with venison jerky and found deer droppings that tested positive for E. coli O157:H7. Deer were also the likely source of  the 1996 outbreak of E. coli O157:H7 in unpasteurized Odwalla apple juice that sickened 76 and killed a child.

On Friday, the Oregonian’s Lynne Terry reported that 10 percent of the samples collected by Keene from the Jaquith Strawberry Farm, including deer feces, tested positive for E. coli O157:H7; further testing will determine if the positive samples match the outbreak strain.

“We’re increasingly confident that we will be able to prove beyond any reasonable doubt that deer were the source of contamination of the strawberries,” Keene told Terry.