Five things you need to know about ice cream and listeria

With another recall of ice cream announced on Friday over fears of listeria contamination _ the third in less than six months _ consumers are wondering whether it’s safe to indulge in their favorite summer treat.

Here are five things you need to know about ice cream and listeria:

- What brands have been recalled so far?

There have been three major ice cream recalls for listeria contamination in recent months, starting with Snoqualmie Ice Cream, a Washington state company that issued a voluntary recall in December for all its products from January 1, 2014, until December 21, 2014.

On April 20, Blue Bell Creameries recalled all of its products currently on the market, including ice cream, frozen yogurt, sherbet and frozen snacks. At least 10 people have been sickened by Blue Bell products contaminated with listeria in Arizona, Kansas, Oklahoma and Texas. Three people died in Kansas.

Jeni’s Splendid Ice Creams on Friday announced a voluntary recall of all ice creams, frozen yogurts, sorbets and ice cream sandwiches for all flavors and containers.

Consumers should not eat any of the recalled products.

- What is listeria and why is it dangerous?

Listeria monocytogenes is a germ that can contaminate food and cause a deadly infection called listeriosis that is characterized by high fever, severe headache, stiffness, nausea, abdominal pain, and diarrhea. Babies, seniors and people with weakened immune systems are particularly susceptible. Listeriosis also has been known to cause miscarriage or still birth if consumed by pregnant women _ a particular concern now for expectant mothers craving ice cream.

“We see listeria associated with lots of other foods out there, and now we’ve added ice cream to the list,” said Doug Powell, former professor of food safety in Canada and the U.S. who publishes barfblog, a food safety blog.

- Can listeria be killed?

Listeria can be killed with heat, but not cold.

“Listeria grows slowly at refrigeration temperatures and it persists in frozen foods,” said Benjamin Chapman, a food safety specialist at North Carolina State University.

- How did the listeria get into the ice cream?

No one really knows for sure yet. The companies and federal food safety experts are investigating.

Ice cream typically is a pasteurized milk product. That means the milk used to make the ice cream is heat-treated to kill pathogens such as listeria before it is frozen. But there are other ingredients that go into ice cream as well that could be a source of listeria, such as flavorings. At least one Blue Bell product that tested positive for listeria contained cookie dough.

Among the possibilities being explored in the Bluebell case is a post-pasteurization contamination. In that scenario, after the milk has been been heat-treated, the ice cream product could have become contaminated in the processing line.

“The plant has lots of equipment that has to be cleaned and sanitized. If it’s not cleaned and sanitized the listeria is establishing a niche,” Chapman said.

Listeria likes to be in cool damp dark places, he said, so something like a drain is a place where listeria might hide.

“So you could see how during a cleaning, they could be spraying hoses, spreading stuff around,” Chapman said. “Or it could be that a piece of equipment was moved and it disrupted a niche of listeria, so the listeria could be in one spot in a piece of equipment, then you shake that up a little bit and it moves the listeria away from its niche and then maybe it leaks into the product.”

- Is it safe to eat ice cream?

Food safety experts Powell and Chapman both said yes.

And Kate Connors, a spokeswoman for the American College of Obstetricians and Gynecologists, said Friday that she didn’t know of any plans to add ice cream to the list of foods pregnant women should avoid eating.

Obviously consumers should toss any of the products affected by the recalls, but listeria is so rare that it simply doesn’t make sense to get rid of all frozen treats in your fridge, said Powell.

“I don’t think there’s a big cause for worry,” he said, “but I do think its incumbent on the companies to do the proper testing and to make it public if they want to not only maintain but ensure consumer trust.”

This story was originally published April 24, 2015 at 1:04 PM.