A lot of people think that the dirtiest area in a house is the toilet (understandably). Actually studies have shown that kitchens contain more bacteria than bathrooms. Just a cutting board alone can have up to 200 times more bacteria than a toilet seat.
One study asked 22 families to send in swabs from different areas around their house, 75% of the kitchen sponges contained Coliform: A bacteria found in human and animal colons and an become a serious contaminant when found in water or food. I have read that if you soak the sponge and put it in the microwave in high for 1 minute it can kill the bacteria and extend the life of the sponge, but the best option would be to change them out regularly.
Cutting boards should be replaced when they get old and the knife grooves get too deep because they become hard to clean inside. You could wash them with vinegar to help fight the bacteria as well. It also helps if you use certain cutting boards for meat and different ones for everything else.
Trash cans are a forgotten area that contain excessive amounts of bacteria due to food falling outside the bag, and should be cleaned about once a month.
The kitchen sink also has a lot of bacteria in and around it due to food being washed off and dishes being rinsed. I suggest the sink should be cleaned daily.
Fridge handles get forgotten a lot, they collect a lot of bacteria because everyone in the house touches them. Washing them once or twice a week would be a good habit to get into.
Coffee makers- NSF international conducted a study and found that half of the coffee pots they studied had yeast or mold growing in the water reservoir. They also had a higher germ count than both bathroom door handles and toilet seats. The carafe, lid, and basket should be cleaned daily. The reservoir should be cycled through with vinegar about once a month depending on how often you use it. This breaks down the calcium and cleans the bacteria out at the same time.
Stove Knobs, cabinet handles, light switches are all high touch areas that are also very forgettable when you're cleaning because they are small areas but they make a big impact. Hands can carry a plethora of bacteria and viruses that can be passed from person to person very easily.
Lunch boxes can carry a notable amount of bacteria because they carry a lot of food that sometimes gets left in there for a while. Cleaning them with soap and water every Friday would be a good way to keep the bacteria at a minimum.
Areas outside of the kitchen that are also often forgotten when clean are:
High touch areas such as computer keyboards, cell phones, TV remotes, stair railings, and faucet handles.
The bedside table cup of water. As soon as you take a sip, your lips and mouth introduce microorganisms to the water. Combined with the ambient temperature in your home and sunlight streaming into your windows, those microorganisms could start to multiply quickly. Emptying it every day and getting a new glass are some preventive measures you can take to ensure you don't get sick.
Washing Machines should be cleaned out once a month, if your washer doesn't have a self clean cycle there is a product called afresh that I read does a good job. Under the rubber seal there is a lot of hair, lint, and soap residue which is a feeding ground for bacteria. Same goes for the soap tray where you add your detergent.
Pet bowls and pet toys may seem like a obviously dirty area to people who don't own pets but us pet owners get complacent with our dirty animals. Spraying their toys with probiotic spray or washing them with soap and water, and washing their bowls out everyday will keep our friends healthy.