Fungal Contamination in Public Buildings: Health Effects and Investigation Methods

2. Health Effects of Indoor Molds

Photo: Dr. Amanda Wheeler

Since 1982, in Europe and North America, approximately 30 studies have been conducted on the association between dampness, mold and respiratory health in residential housing. Studies in the United States and Canada have involved the largest number of people. A study of the respiratory health of 4,600 children from six cities in the northeast United States demonstrated that the presence of mold and dampness in their homes was correlated to several respiratory symptoms as well as a number of non-specific symptoms. The effect on the children was of similar dimension to parental smoking (Brunekreef et al. 1989). Two studies involving 15,000 children and 18,000 adults from 30 communities in Canada came to similar conclusions. The authors suggested that a non-allergenic mechanism may be involved since there was no effect modification by reported atopy and asthma. A dose–effect relationship was also seen in that more visible mold yielded more symptoms. Overall, the mold contamination was associated with a 50% relative increase in asthma and a 60% increase in upper respiratory disease (Dales et al. 1991a, 1991b). Data from a further 13,000 children from 24 cities across the United States (19 cities) and Canada (5 cities) show the same pattern (Spengler et al. 1994). The upper boundary attributable risk for mold-caused asthma in Canada was estimated at 20% (Dekker et al. 1991). The health effects of fungal contamination in housing remain significant even after adjustment for socio-economic factors, pets, household smokers, endotoxins and dust mites (Dales and Miller 1999; Dales et al. 1999).

A review published in 1995 by Health Canada and the Federal-Provincial Advisory Committee on Environmental and Occupational Health (CEOH) concluded that “. . . epidemiological studies have consistently detected an association with respiratory symptoms and home dampness and mold growth, but causality in these studies has not been established” (CEOH 1995a). The evidence linking exposure to indoor molds with adverse respiratory outcomes has also been reviewed by Verhoeff and Burge (1997). More recently, the US National Academy of Sciences Institute of Medicine released a report on asthma entitled Clearing the Air: Asthma and Indoor Air Exposures. The panel found that there was insufficient evidence on a population health basis for the association between indoor residential molds and the development of asthma, but that indoor mold was associated with exacerbation of asthma in mold-sensitized individuals, and exposure may be associated with respiratory symptoms. The percentage of mold-sensitized asthmatics is not known; estimates range up to 40% (Institute of Medicine 2000).

The purpose of this section is to update the review conducted by the Federal-Provincial Advisory Committee on Environmental and Occupational Health (CEOH) in 1995 by reviewing the research published since then on health effects due to exposure to molds in residences and nonindustrial workplaces (mostly office buildings and schools), and to determine whether the current evidence warrants more definitive conclusions. Following a summary of studies published since 1995 (section 2.1), some potential effects of molds in sensitive sub-populations are discussed (section 2.2), followed by an overview of the experimental studies on respiratory effects of molds (section 2.3) and a discussion of the evidence linking mold exposure to adverse health outcomes (section 2.4).

Health problems, such as hypersensitivity pneumonitis (HP) and organic dust toxic syndrome (ODTS) identified in industrial and agricultural settings due to greater exposure to molds (and, in some instances, other biological contaminants such as thermophilic actinomycetes), will not be discussed here.

2.1 Epidemiological Studies of Respiratory Illness

In order to review recent cross-sectional and cohort studies on health effects of indoor molds, Medline was searched using the following keywords: fungi, or mold, or mold and respiratory tract diseases. Articles published in 1995 or later pertaining to cross-sectional, cohort or case-control studies assessing the association between indoor exposure to molds (visible mold growth or airborne fungal cell counts) and asthma or related respiratory symptoms were included in the review. Studies with no mold exposure variable (e.g. those considering only dampness) and prevalence studies with no measure of association were excluded.