Fungal susceptibility score: an innovative criterion for risk assessment of indoor airborne fungi for people and items

Indoor air often contains spores and fungal propagules, which generally do not present significant risks to people or items. However, increasing humidity and temperature can boost fungal growth, suddenly changing the environmental scenario. The present work reports a mycological survey carried out in an attic apartment in Genoa (Liguria, Italy). We performed both direct surface examinations of visibly contaminated areas and air sampling using a Surface Air Sampler (SAS) in duplicate with two different culture media. The SAS air samples revealed a high concentration of CFU/m³ with the maximum concentration of 2085 CFU/m³. The qualitative analysis, initially performed through morphological identification and subsequently confirmed using molecular methods, identified a limited number of species with a high-risk factor for humans and/or materials. In this context, to make an overall risk assessment for people and items, we proposed a new criterion called Fungal Susceptibility Score (FSS) based on the relative abundance and functional traits of the isolated fungal genera. The results obtained underscore the importance of considering all taxa detected in the investigated area, not only their potential pathogenicity to humans. This work also introduces a criterion that correlates the ecological characteristics of genera present in a specific environment with their abundance, aiming to objectively assess the level of risk for both humans and objects. The FSS provides a reproducible metric to assess fungal risk in indoor environments.