Sanitation of wallboard colonized with Stachybotrys chartarum

Sections (8 cm(2)) of unused, nonsterile gypsum wallboard (dry wall) were i noculated with varying densities (10(4) to similar to 10(8)/ml) of conidia from 14- to 21-day cultures of Stachybotrys chartarum grown on cellulose ag ar. The sections were permitted to air dry and were placed into vessels wit h 86% or 92% RH and incubated at 22-25 degrees C for up to 12 weeks. The mo isture content of the dryboard increased from near 10% to over 35%, Selecte d sections with confluent surface growth, mainly of S. chartarum, were obta ined within 3 weeks. Sections were cleaned with a quaternary or quaternary and chlorine dioxide or a concentrated oxygen-saline solution and treated, in some cases, with a preservative system and returned to humidity vessels. Reemergence of S, chartarum from inoculated and treated surfaces occurred within 5 weeks only with sections treated with the quaternary alone. Other fungi, mostly species of Aspergillus, Chaetomium and Penicillium, slowly co lonized (between 9-12 weeks) at least some areas of most treated surfaces a nd most uninoculated control surfaces. Stachybotrys chartarum was also foun d on several sections of uninoculated controls. Sections treated with a qua ternary/acrylic and placed in a dynamic challenging chamber remained visual ly free of colonized fungi for over 90 days. These studies indicate that co ntrol samples of uninstalled wallboard, available from local distributors, can contain a baseline bioburden, including S. chartarum, that will coloniz e surfaces under high humidity conditions. Sanitation and preservation trea tment of the wallboard can markedly delay regrowth of these fungi, particul arly of S. chartarum.