In order to prevent or remove concentrations of mold, bacteria, and other biological pollutants, you first need to understand how these microorganisms grow. Biological contaminants thrive in moist environments. Bacteria, mold, fungi, and other such nuisances can grow out of control in such conditions. While warmth can also contribute, it is often the colder weather or air conditioning that can worsen the problem because as the air cools, it can hold less moisture, thus causing condensation to develop in potentially hidden areas. Cold windows, for example, can cause a collection of moisture and often grow mold around their perimeter.
To prevent moisture and thus reduce the opportunity for biological contamination, there are several steps homeowners can take. Start by checking the home for leaky doors and windows. Check for water leaks in basements and around pipes in the kitchen and bathroom. Seal any cracks with caulk or other sealants.
Exhaust fans in kitchens and bathrooms help to remove humid air and prevent mold from forming. These fans should be directed outside, not into the attic. The clothes dryer also needs to vent outside. Crawl spaces should be well-ventilated and may benefit from having a plastic ground covering to prevent ground moisture from getting up into the house. Dehumidifiers are recommended in areas that are particularly moist, but they must be kept clean and well-maintained.
Use insulation or double-paned windows to prevent cold from creeping inside and causing condensation. Open doors to closets that face outside and rooms that do not have air vents to prevent temperature differences. Carpet on concrete floors is a recipe for moisture and mold; it is far better to first lay a vapor barrier and sub-flooring before installing carpet. Dust and clean regularly, including all appliances and areas that come in contact with water. Finally, using a high-rated filter in the HVAC system can help eliminate biological contaminants that are already circulating in the air supply.