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Cross Contanimation: Causes & Types

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson briefly defines cross-contamination before going over the major causes of cross-contamination as well as some of the major types of cross-contaminants we need to be worried about.

Cross Contamination

One of your parents likely told you to wash your hands before you eat ever since you were a little kid. But did you ever stop to think of why they kept harping on and on about that? It's because that parent wanted to avoid cross-contamination, the transfer of disease causing agents from one surface/object to another. That includes the surface of your hand to the surface of something like the Cheerios you were going to stick in your mouth, or nose. This term is mainly used with respect to cross-contamination as it applies to food.

The Cheerios in this bowl could be affected with cross-contamination
bowl of cheerios

In this lesson, we're going to go over the major causes and types of cross-contamination in that respect.

Causes of Cross Contamination

So what are the major causes of cross-contamination? One very big one relates to our Cheerios example in our introduction, the improper washing of things like our hands. Dirty hands contain lots of microbial agents, like bacteria, which can be transferred to a sandwich we're holding, or vegetables we're cutting into a salad, and so on.

Our hands aren't solely to blame of course. If we improperly wash the produce (as in, the fruits and veggies) that we'll be eating, it doesn't matter how clean our hands are. That produce will have lots of germs on it that can then contaminate potentially clean things, like kitchen countertops.

And if you don't properly wash kitchen surfaces and place something like a relatively clean piece of bread onto one then, guess what? That bread will be cross-contaminated with germs! You probably get the idea here with respect to improper washing of things leading to cross-contamination.

Another important cause of cross-contamination is improper cooking. Let's say that you've decided to grill some chicken and make a salad. You take a cutting board and start cutting the raw chicken into strips. Then you take out and wash the produce you're going to use for the salad. You put that clean produce onto the same cutting board you used for the chicken. Bad idea!

Even if you rinsed or washed that cutting board after cutting the chicken on it, that's still not good enough. The cutting board may have microscopic cuts in it where microbes can hide even after washing. The microbes will then be transferred to the clean produce and contaminate it in the process. So, proper cooking technique is imperative to avoiding cross-contamination! In this case, that involves using two different cutting boards. One for meat and the other for produce.

The third major cause of cross-contamination is improper storage. Let's say that you wanted to thaw some raw meat. You take the meat out of the fridge and place it on a dish. You then place the dish in the fridge. The problem is that that dish is pretty shallow and as the meat thaws it releases a lot of water and juices that overflow and spill all over the fridge. All that liquid is full of germs that contaminate the food in the fridge, the surfaces of the fridge, and any food that later comes into contact with those surfaces. Proper storage in this case would involve a deeper and leak-proof container.

Raw meat like this must be stored properly to avoid cross-contamination
raw meat improperly stored

Types of Cross-Contamination

So now that you know a bit about the causes of cross-contamination, what types of contaminants do you need to worry about? The major one is bacteria. This includes the likes of E. coli, Salmonella, Listeria, Clostridium, and Campylobacter, among a sea of others.

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