State health officials are investigating six cases of salmonella poisoning linked to a recall of organic eggs, said the Minnesota Department of Agriculture (MDA) said in a news release.

The tainted eggs have been traced back to Larry Schultz Organic Farm in Owatonna, where testing confirmed the presence of salmonella bacteria. The farm has issued a voluntary recall of the eggs and is cooperating with the investigation.

According to the news release, at least six people, both children and adults, became ill between August 12 and September 24 after consuming the organic eggs, which were sold at grocery stores under the brand names Lunds & Byerly’s Organic, Kowalski’s Organic and Larry Schultz Organic Farms.

Affected eggs were sold in 6-egg cartons, dozen egg cartons and 18-egg cartons and carry the EXP Nov 12 label. (Cartons bearing plant number 0630 or a “Sell by” date are not included in the recall.) They were distributed to restaurants, grocery stores, food wholesalers and food service companies in Minnesota, Wisconsin and Michigan.

Salmonella can cause serious and sometimes fatal infections in young children, frail or elderly people, and others with weakened immune systems.  Symptoms include fever, diarrhea (which may be bloody), nausea, vomiting and abdominal pain.

Health Department epidemiologist Trisha Robinson said the bacteria can affect all kinds of eggs, regardless of whether they’re conventional, organic or free-range.

“It’s just a great reminder for every egg consumer that they should thoroughly cook their eggs and that means that both the yolk and the white should be cooked thoroughly through until they are firm,” she told MPR News.

Consumers who believe they may have purchased the affected eggs should not eat them but should return them to the store where they were purchased for a full refund. For more information, view the full recall at the Minnesota Department of Agriculture website.