Wall relative humidity: a simple and reliable index for predicting Stachybotrys chartarum infestation in dwellings

Because the indoor mold Stachybotrys chartarum has been considered as potentially responsible for serious health effects, its identification in dwellings with water damages is of utmost importance. As such dwellings are many, it would be of great value to have a simple and reliable index for predicting its presence. The aim of the study was to compare measurements of wall relative humidity (RH) to mold identification in 458 samples from 100 dwellings. Mold identification was performed by direct microscopic examination of a sample collected on the wall by the gummed paper technique. Mean (+/- s.d.) wall RH (%) was much higher (97.0 +/- 6.1) on the 30 samples where S. chartarum was identified compared with the 291 samples where other molds were identified (41.8 +/- 36.9) and to the 137 samples where no molds were identified (38.9 +/- 34.8). There was no straightforward relationship between wall and room RH. In conclusion, this study clearly demonstrate that the simple measurement of wall RH can be used as a reliable index for discarding and suspecting S. chartarum infestation in dwellings.

This paper suggests that very high relative humidity (RH) within walls is a strong risk factor for their infestation with the 'toxic mold' Stachybotrys chartarum. Besides, data from the literature demonstrate that other molds are able to produce mycotoxins when RH is very high. Thus, measurement of wall RH, which is easy to perform and very cheap, could be used as a screening tool to select those dwellings where mold identification should be performed and remediation should be promptly carried out.