Bacteria, fungi, mold and yeast are commonplace. Even on surfaces that appear visibly clean. Microbes can live on doorknobs, handles and commonly touched surfaces indefinitely sometimes in a dormant manner (see Germophobic.net). Some molds like can have long term consequences on your building structure and cause wood to rot. Resident bacteria can be the cause of corrosion of metals. (Some references for understanding how microbes may impact materials are e.g Fontana and Green, Corrosion Engineering (book), McGraw Hill Publications, additional references are listed in several review articles including http://www.scientific.net/KEM.521). Your local library may be able to obtain these reference materials for you.
According to the website Germophobic.net, more bacteria live on a well-used door knob than on your toilet seat. The same goes for the kitchen sink, especially around the faucets and in the drain. The “Health” magazine senior editor warns that your sink drain can harbor up to 500,000 bacteria per square inch. Not all microbes are harmful but if you find yourself with an overgrowth threatening the health of your family, frequent cleaning with a disinfectant and/or MightSteam™ is one way to control the problem. When steam is employed as an antimicrobial agent please try and use highly superheated-steam if available for your use. Regardless of what one reads, one should not develop a phobia (http://en.wikipedia.org/wiki/List_of_phobias) but instead consider positive ways to reduce any dangerous microbes.
But how do you guess the frequency of cleaning required and whether your cleaning method is adequate? The best solution is to work with a microbiologist – however some easy test kits are also available. To see how dirty your surfaces really are, consider testing them with any of the methods below or by serching for tests kits on search engines. There are a number of inexpensive test kits available to test many surfaces. Some of the popular ones are listed below. Kit manufacturer should be able to directly give you more details on reliability, allowed use and other specific details for viruses, bacteria, molds and yeasts.