GEOFF BENNETT: A deadly E. coli outbreak linked to a popular McDonald's menu item is the latest in a number of cases involving dangerous foodborne illnesses.

It's prompting concerns and questions over the safety of our food supply.

Stephanie Sy has more.

STEPHANIE SY: Geoff, federal officials are investigating a deadly E. coli outbreak linked to McDonald's Quarter Pounder hamburgers.

At least 49 people have gotten sick in 10 states and one person has died.

McDonald's says it serves about one million Quarter Pounders in those combined states every two weeks.

The company believes the food poisoning is tied to sliced onions on the burgers supplied by a single vendor.

McDonald's USA President Joe Erlinger spelled out in a video for customers what the company is now doing.

JOE ERLINGER, President, McDonald's USA: We have taken steps to proactively remove slithered onions, which are used in Quarter Pounders, from restaurants in select states.

We also made the decision to temporarily remove the Quarter Pounder from restaurants in select states.

The decision to do this is not one we take lightly, and it was made in close consultation with the CDC.

STEPHANIE SY: Erlinger also said McDonald's' other meat products are safe and will continue to be sold in those states.

For more on this case and ongoing concerns about food safety, I'm joined by Donald Schaffner, who's focused on this subject at Rutgers University.

Don, thank you so much for joining us.

With this case, many of us will remember the Jack in the Box hamburger outbreak of E. coli that occurred in the early 1990s.

This case with McDonald's doesn't seem to rise to that magnitude.

Still, as somebody who studies these incidents, how surprised are you that this outbreak is occurring at McDonald's, essentially an American institution?

DONALD SCHAFFNER, Rutgers University: Yes, I'm really surprised that it was McDonald's that got hit by this particular problem.

They take food safety very seriously.

They put a lot of pressure on their employees and on their suppliers to make sure that stuff like this doesn't happen.

STEPHANIE SY: We should say that the outbreak appears to be in the past tense, from what we know, occurring between September 27 and October 11.

Don, is it normal to have that lag time between when people start to get sick from a food product and when the public hears about it?

DONALD SCHAFFNER: Yes, so the CDC is working all the time to take isolate, stool isolates, and do whole genome sequencing.

But it takes a while to put together a picture to say, hey, all of these people are all getting sick around the same time and they're all sick from the same organism.

Then they have to go and talk to these people and say, hey, what did you eat however many weeks ago and what do you remember about that?

And then bit by bit, they put the pieces together.

And then, when they're sure, when they're confident or mostly confident, that's when they go public.

And that's what happened recently here.

STEPHANIE SY: And, as you know, Donald, the McDonald's case is just the most recent outbreak of foodborne illness.

Over the summer, we had Boar's Head deli meats contaminated with listeria.

That has been linked to 10 deaths.

Go back and tell us what we know about what happened at Boar's Head and how that contamination occurred and spread.

DONALD SCHAFFNER: Yes, well the Boar's Head situation is very different than the current situation.

first of all, it's a different regulatory agency.

Meat and poultry are regulated by USDA Food Safety Inspection Service.

They have inspectors continuously on site.

It sounds like there were, based on Freedom of Information Act requests, reading the N.R.

notices that were issued to that plant, it sounds like that that particular plant had a systemic and ongoing food safety problem, whereas this just appears to be a temporary blip.

STEPHANIE SY: Well, let's talk a little bit more about that, because there were repeat violations that one of Boar's Head production plants, with reports revealing -- and this is going to grow some folks out, but the reports revealed mold, insects, dripping water and meat and fat residue found on the walls of the facility dating back two years.

Why wasn't that facility shut down?

Did somebody drop the ball at the USDA?

DONALD SCHAFFNER: Well, that's -- why wasn't the plant shut down is a good question to ask USDA.

Now, making meat is a messy business, and you are going to have occasional problems.

But, having said that, having read those N.R.

reports, this does seem like it was an ongoing problem, so, yes, so definitely some questions that USDA needs to answer there.

STEPHANIE SY: There are, of course, victims when companies don't keep food safe, and, of course, there are lawsuits, legal settlements.

We can look at the stock price, McDonald's down 5 percent today.

Are there enough actions being done, though, to prevent foodborne illnesses from occurring and for there to be more accountability?

DONALD SCHAFFNER: Well, I think regulatory agencies and FDA in particular could always use more resources.

Mostly, especially with FDA-regulated products, they really rely on the companies knowing what they're doing and doing a good job.

Now, we still don't know exactly what happened in this particular case, but there may be some implications.

Certainly, if I was somebody who bought onions and who bought sliced onions, I'd be looking carefully at my supplier.

If I was an onion supplier, I'd be looking carefully at where I get my onions from.

We need to figure out where this particular problem came from.

And then, once we know where it came from, then we can begin to put steps in place to prevent it from happening again.

STEPHANIE SY: I'm just thinking through that.

I think, for the average consumer, it might be difficult to know how to know whether a vendor of onions or any particular food is safe.

So I go back to the question of whether these incidents should concern us broadly about food safety and enforcement in this country.

DONALD SCHAFFNER: Well, I think that people are right to be concerned.

But, at the same time, I will say that most everybody eats food most every day and most people don't get sick most of the time, right?

And so -- but, obviously, we're concerned about these situations where stuff goes wrong.

The thing is, we have good rules in place, but we need to make sure that those rules are followed and that we have adequate inspection resources and that companies know what their responsibilities are to make sure that everyone does what they need to do to keep the food supply safe.

STEPHANIE SY: Donald Schaffner with Rutgers University, thanks so much for joining us.

DONALD SCHAFFNER: My pleasure, Stephanie.

Thanks.