Raw milk from a farm near Brookings tested positive for Listeria earlier this week.
So what is Listeria and why is it dangerous?
It is a bacteria that can cause flu-like symptoms in relatively healthy people, but can be serious for people with weakened immune systems.
Listeria threatens pregnant women most.
Doctor Lon Kightlinger, the state's top infectious disease expert, said a mother may feel fine, while it attacks the fetus.
"One of the things that Listeria likes is fetal tissue. It'll zero in on a fetus and cause miscarriages, spontaneous abortions, or still birth or premature delivery."
If Listeria is found, it is more likely to be in raw milk.
"Raw milk would be fresh off the cow, even what's stored in the tank here, that's raw milk. Once it becomes processed at a processing plant, pasteurized would be the main thing, then it's no longer raw milk." Said Craig Krogstad.
When it is pasteurized, the milk is heated up to a temperature that kills the all the bacteria, makes it safe to drink and increases shelf life.
Krogstad works at a farm that pasteurizes it's milk.
He said keeping the milk safe starts with the cows, "All of our cows here have been raised on this farm for several years now, so I know the health history of them. So we vaccinate them, do preventative treatments with the calf and cows to keep them healthy. Healthy cows are productive cows."
The Brookings County milk that had Listeria in it, was found at a raw milk farm.
That milk isn't processed like Krogstad's.
"If there's high bacteria and it gets kicked out and I get notified that something is wrong here and I have to fix something." He said.
To ensure that doesn't happen, his farm cleans the cows a lot.
"We clean the cows prior to milking the cow and attaching the unit, and then after the cow is done milking, we use a disinfectant after milking, we call it a post dip, and that's to prevent any bacteria pathogens from getting into the cows utter, so she doesn't get sick. It keeps the milk clean." Krogstad said.
He added even though he does not produce raw milk, the Listeria is a reminder that he needs to keep his standards high.
But he adds this one incident doesn't mean people should be scared.
The milk in question came from Jerseydale Farm near Brookings.
If you have that brand of raw milk, the State Health Department said you should return it or just throw it out.