When you think about the dirtiest places in your home or office, is the microwave on your list? It should be. Bacteria can be left behind in spills or splatter from food, and a variety of microorganisms may be found on the outside surfaces that are touched over and over again.
A swab study completed by Kimberly Clark surveyed almost 5000 locations in a variety of office settings.1, 2 48% of the microwave door handles tested had ATP counts of 300 or higher. ATP, or adenosine triphosphate, is a molecule that provides the energy needed for living things and can be used to assess how dirty a surface is.3 While an ATP count of 100 to 300 indicates a surface needs more frequent cleaning, an ATP count of 300 or greater indicates a dirty surface that has a high risk of illness transmission.1
Another swab study conducted in a residence in Miami found E. coli inside the microwave.4 Dr. Julie Torruellas-Garcia and her students analyzed the samples collected from the home. She explains, "We use it [the microwave] to cook our food, but also to defrost meat. Raw meats carry bacteria like E. coli and Salmonella. Sometimes, the food splatters around the microwave and we don't always clean it."
Food spills in the microwave are bad in a number of ways. They provide nutrients for bacterial growth. They can lead to offensive odors when reheated, and catch fire in a worst-case scenario. They can decrease the efficiency of the microwave. And they get harder to clean each time they are heated.5
So, what can be done to clean up this microbial hot spot? Regular cleaning and disinfection of the outer surfaces, including the handle and keypad is a must. For the inside, set food on a microwave-safe plate and cover it during the cook time. And clean up any spills or splatters as they occur. Use warm water and a mild soap like dishwashing liquid to clean the interior periodically.5, 6
3. http://www.hygiena.com/frequent-asked-questions-food-and-beverage.html, What is ATP monitoring?
6. Some tips for the dried-on gunk: http://www.ehow.com/list_6711549_ways-clean-microwave-oven.html