The \'dirtiest\' places in your house!

What do you think are the dirtiest places in your house? Naturally, by 'dirty', I do not refer to a prevalence of that dusty substance that seems to envelop everything, but rather an infestation of millions of squirming micro-organisms. Some of these micro-organisms can be harmless, but others could cause serious discomfort. Would you wager that a toilet is cleaner than a keyboard? The inside of the fridge, or something as unassuming as a light switch? Read on and find out.