The problems have been attributed to the use of fly ash in the drywall, which degrades in the presence of heat and moisture; although United States' drywall uses fly ash as well, the process used creates a cleaner final product [REF].
According to a 2010 laboratory study, one hundred percent of affected drywall samples obtained from homes located in the southeastern United States tested positive for the presence of Acidithiobacillus ferrooxidans, an iron and sulfur reducing bacterium.