Nothing really beats the convenience of prepackaged, pre-washed greens -- especially is you're cooking for a big family or don't have a whole lot of time on your hands.

In fact, more than 70% of U.S. households consume packaged or bagged salads -- which make up part of a nearly $7 billion industry.

But considering all the reports of diseases and other potentially harmful and unhealthy things that may be lurking in those prepackaged bags -- on top of the fact that you're supposed to wash the contents anyway -- they may not always be the safest choice.

The potential health risks 

According to the CDC, Listeria is a harmful germ that can hide in many different types of foods.

When food contaminated with the germ is consumed, it can lead to a serious infection called listeriosis -- which causes 1,600 illnesses and 260 deaths every year, according to the CDC.

While anyone can get sick, the CDC says the infection "is most likely to sicken pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems."

Why you need to be careful with prepackaged lettuce/salad

The problem is, while many packages contain "pre-washed" greens, sometimes even "triple washed," they can still contain harmful disease-causing bacteria, like Listeria, salmonella or E. coli, which can't always be rinsed off.

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After an outbreak a few months ago, the CDC issued a warning that “consumers do not eat, restaurants do not serve, and retailers do not sell packaged salads" that were produced at the same facility where Listeria was found. 

Prepackaged vs. non-packaged greens

So why is bagged lettuce more at risk of containing bacteria than a regular old head of lettuce you buy at the store?

Bagged greens typically contain younger leaves, which have a higher risk of contamination. According to Jeri Barak, associate professor of plant pathology and executive member of the Food Research Institute at the University of Wisconsin-Madison, “Data suggests that bacteria (Salmonella and E. coli) can enter wounds, such as the harvesting cut, and travel some distance into a leaf. But fresh produce that’s harvested as a head has longer leaves and is more mature. A consumer has the opportunity to remove part of the head away from the harvest cut and eat leaves in which a pathogen did not reside in the harvest wound.”

On top of that, a lot more steps are required to get bagged lettuce from the harvesting stage to your local grocery store -- which means more opportunities for contamination. Plus, many prepackaged greens contain more than one type -- so spinach carrying bacteria could not only contaminate bags of spinach, but it could also contaminate bags of mixed greens and any other packages containing the same spinach.

Some research suggests that the inside of the bags can even foster the growth of bacteria.

And don't assume organic greens are exempt -- they are no more or less likely to carry harmful bacteria.

So when it comes to bagged greens, the health risks are still low, but if you have the option of choosing prepackaged or non-packaged, the latter is the safer choice -- and you should still rinse and clean the produce as thoroughly as possible.

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