Standard S520, the Mold Remediation Standard, has been developed by the Institute for Inspection, Cleaning and Restoration Certification (IICRC) in order to address these questions, as well as to provide a "standard of care" for the many industries involved in mold and moisture remediation, including HVAC contractors. It uses the term "fungal ecology" to describe the mold content of a particular area.
Acknowledging that we live in - and have always lived in - a fungal ecology, the standard describes varying degrees of the ecology and provides input on fungal ecologies that may or must re-quire remediation. In short, it uses common sense.