But officials aren't sure if the bacteria was on the steaks when the meat was shipped to the store, or if a metal tenderizer machine that Costco had used pushed E. coli into the steaks.
Dr. Gerry Predy, Alberta's senior medical health officer, says it may be impossible to determine the source of the E. coli contamination.
"The E. coli had to come from somewhere," he said Wednesday at a news conference.
"Some of the meat that was used in that particular machine must have had E. coli on it. Whether the steaks actually had the E. coli on them or were just contaminated because the machine was contaminated — that is something that we will probably never know for sure."
Predy declined to say how sick the four people in Edmonton are who have the bacterial infection, citing privacy concerns.
He provided no information about four other E. coli cases under investigation, including three in Calgary and one in central Alberta.
The Canadian Food Inspection Agency says the steaks sold at the Costco outlet came from meat slaughtered at the XL Foods Inc. plant that is involved in an extensive ground beef recall throughout Canada and eight U.S. states.
CFIA spokesman Tim O'Connor said agency investigators are trying to pinpoint where the Kirkland brand strip loin steaks were tainted.
"The recalled steaks were produced by XL Foods. At this point we don't know definitively where the E. coli contamination occurred," he said from Ottawa.
"There is a lot of variables between where it would have been slaughtered and retail. Where was it further processed. What other products could it have come in contact with between slaughter and retail."
XL Foods Inc. said in a statement issued late Wednesday that the company is working with CFIA and Alberta Health Services to understand more about the steak recall from the Edmonton Costco store.
"Even though there has been no definitive link of illness between our products and people who have become ill, we are very concerned for their well-being and (are) working in their best interests. Our thoughts are with those who have become ill at this time."
XL Foods also said it will continue to keep customers and consumers informed when investigation findings become available.
Since Sept. 16, the CFIA has issued at least seven recall alerts for XL Foods Inc. ground beef products from its Lakeside plant over E. coli concerns. There are no reported cases of people getting sick from eating the ground beef.
Canada revoked the plant's permit to export beef to the U.S. on Sept. 13 at the request of the U.S. Department of Agriculture.
XL Foods said there were two deficiencies cited by the CFIA in the ground beef recall — the first, it says, was the application of trend analysis performed by the company, and XL Foods said it has developed a plan "that exceeds industry standards and has been accepted by CFIA."
The second deficiency, XL Foods says, related to documentation of process.
"XL has implemented increased documentation processes to comply with CFIA requests. By developing these enhanced measures XL will increase the level of food safety," the statement said.
The CFIA alert issued Wednesday morning warns people not to eat the brand of beef steak sold in the Edmonton 50th Street Costco because it may be contaminated with E. coli. The steaks were sold and packaged between Sept. 4 to Sept. 7.
E. coli O157:H7 is potentially deadly. Health officials say it can cause bloody diarrhea, dehydration and, in the most severe cases, kidney failure.
Predy said investigators were able to test an uncooked steak that came from a package of Costco steaks and compared it to a sample from a person who got ill eating another one of the steaks.
"The lab did confirm that not only was the steak growing E.coli, but it was the same genetic pattern as the individuals who were ill."
On Wednesday, the U.S. Food Safety Inspection Service (FSIS) issued a release that says whole cuts of beef were produced at the XL Foods plant on the same production dates as the suspected tainted ground beef.
The meat cuts were used by a U.S. manufacturer to make other food products, which have not been identified.
U.S. food inspectors say that information from the Canadian Food Inspection Agency leads them to believe "that beef from cattle slaughtered during the period associated with the recall was produced under unsanitary conditions that resulted in a high event period ... when trim from carcasses exhibited an unusually high frequency of positive findings for the possible presence of E. coli 0157:H7."
"Because FSIS now has evidence gathered through effectiveness checks that whole muscle cuts were being used to produce ground beef, the agency is issuing this public health alert."
The union that represents food inspectors in Canada is raising questions about a federal government plan to eliminate the inspection of food shipments at some Canada-U.S. border points. It is also speaking out about the practice of allowing the meat industry to partly police itself.
The Public Service Alliance of Canada points out it was tests by U.S. inspectors at a Montana border crossing that first detected E. coli in XL Foods ground beef on Sept. 3.
Union vice-president Fabian Murphy said Canada and the U.S. are negotiating the elimination of the inspection program.
"XL Foods is a perfect example of why we need to keep and strengthen food inspection at the border, not eliminate it," he said Wednesday from Ottawa.
XL says the Lakeside plant is the largest Canadian-owned beef facility and second largest in the country behind U.S.-owned Cargill.
Some cattle producers are wondering how the E. coli recall and export ban will affect their businesses.
Alberta health officials say there have been 66 E. coli cases in the province this year, but the numbers are down from years past because of better food handling and other safeguards.
Predy said Costco said it's no longer using the tenderizer machine.