As a professional carpet cleaner in Tampa FL I get a lot of questions about killing germs in carpet. Many people feel that their carpet harbors a lot of germs and bacteria. They're right. That does not meant that carpet is an unhealthy floor covering. Carpet can do a lot to improve the overall health of your home. It acts a a giant filter trapping dirt and airborne material in it's fibers. It just needs to be maintained on a regular basis by a professional carpet cleaner.
Steam cleaning alone does not kill carpet borne microorganisms. the cleaning solution does get hot enough to kill bacteria and mold, but that heat is not sustained long enough to do any real damage to those microorganisms. The only way to truly clean your carpets and make them healthy again is to use a carpet sanitizing spray to eliminate any pathogens and mold in your carpet.
This video shows you how a carpet sanitizing spray can be used before a professional carpet cleaning. it should be sprayed evenly onto the entire carpet and then scrubbed in to get full coverage. The sanitizer needs to dwell for at least 10 minutes. after which up to 99% of the pathogens will be dead. Then your carpet can be professionally cleaned to remove any excess sanitizer left behind.
Next time your thinking about getting your carpets cleaned consider getting it sanitized as well.