Microbiologic Contaminants include viruses, bacteria, fungal spores, protozoa, algae, animal dander, and animal and insect excreta. They often live and reproduce in microclimates, such as damp basements and bathrooms. Heat exchanger coils and condensate pans, refrigerator condensate and defrost pans, and ductwork often provide microclimates if not installed and maintained properly. Humidifiers which don't heat the water can be a source of microbiologic contamination.
It is important to keep relative humidity under or at 70% to keep materials in the building from absorbing water and supporting the growth of fungi. Condensation can cause humidity levels near surfaces that are cool to rise above 70%. For microbiologic organisms to have a negative impact on the occupants of a building, there has to be an environment favorable to the organism and the occupants must come in contact with the contaminant.