Truth be told, I don't switch out old for new toothbrushes as often as I should. Thanks goodness my dentist hands me a new one every six months when I get a check-up and cleaning. Otherwise it stands in the toothbrush holder less than an inch from my wife's toothbrush which also gets switched out every six months as part of the same routine. Now be honest, it makes you uncomfortable if your toothbrush touches your spouse's toothbrush, right? Yes! God only knows what goes on behind closed medicine cabinet doors! EEEEK! That's the same person you kiss...on the lips... daily... yet this toothbrush thing is a violation. I, as part of the morning and bedtime process, give my toothbrush a thorough rinsing before I begin brushing.
I received some good information this morning about toothbrushes and bacteria that came as a relief. According to Lifehacker your toothbrush is loaded with bacteria, but it's your bacteria! - Matt Appleby
No such thing as a clean toothbrush ... Toothbrushes are gross. We know this. They are bristled petri dishes of bacteria that we continue to put in our mouths, even though we know how disgusting they are. But there's some good news. The CDC says that although there is a ton of bacteria on your toothbrush, most of it comes from your own mouth and is therefore not going to make you sick. In fact, efforts to keep them clean by storing them in containers or keeping them away from the sink, are futile. Actually, you may be supporting the growth of bacteria. The best way to keep your toothbrush clean is to rinse it thoroughly after use and then let it air dry. You may be asking, "Doesn't the toothbrush pick up a lot of icky stuff from flushing the toilet?" The answer is yes, but there's been no research to support that any of it will get you sick. (Lifehacker)