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The word "mold" is a non-scientific term that in popular parlance generally refers to members of a few dozen filamentous fungi. Mold growth on building surfaces not only damages these surfaces, but also affects air quality as intact spores, as well as spore and mycelial fragments, are dispersed in the air. These can be inhaled depending on their size and concentration. Exposure to mold is associated with increased rates of respiratory disease.
This document is a revision of an earlier version published by Health Canada and the Federal-Provincial Advisory Committee on Environmental and Occupational Health (CEOH) in 1995. The intent is to update the information and to reconcile certain practical aspects of the document with newer publications from the American Conference of Governmental Industrial Hygienists (ACGIH), the American Industrial Hygiene Association (AIHA) and other cognizant authorities. The purpose of this document is to assist front-line public health workers in the management of potential health risks associated with fungal contamination in public buildings. The report consists of two parts:
1. A review on health effects of indoor molds
2. A guide for the investigation of mold contamination in non-industrial workplaces
The 1995 review 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." The purpose of this section is to update the CEOH document by reviewing the research published from 1995 to 2001 on health effects of exposure to molds in residences and non-industrial workplaces (mostly office buildings and schools), and to determine whether the current evidence warrants more definitive conclusions.
Major findings from this review are:
Several of the studies reviewed were limited by the methods used: exposure and outcome assessment based on self-reporting; no quantitative exposure assessment (and therefore no determination of a dose-response relationship); possible confounding by other biological agents; and potential response bias.
Only in a few studies reported to date has an independent effect of mold on asthma and upper respiratory health been demonstrated. Therefore, from epidemiologic data alone, it is difficult to assess the population health consequences of the material growth of indoor molds. It is known, however, that exposure to fungi in occupational environments causes allergic and toxic diseases. Adverse effects of fungi have also been seen in inhalation studies using animal models. Therefore, further investigation of health effects of indoor fungi using improved exposure and health outcome assessment methods is needed to resolve uncertainties. As established by the CEOH in 1995, current knowledge indicates the need to prevent damp conditions and mold growth and to remediate any fungal contamination in buildings.
It cannot be emphasized enough that the best way to manage mold growth is to prevent it before it occurs. The essential elements of a prevention strategy are control of moisture, timely remediation of any water leakage, and adequate maintenance of heating, ventilation and air conditioning (HVAC) systems
The goals of a mold investigation are to:
The first step in investigating a building for microbial contaminants is an informed inspection. Mold contamination can arise from condensation, floods and various types of leaks. Investigation of mold problems requires a thorough knowledge of the design of the building envelope and the types of failures that result in condensation and water leaks. Where there is probable cause to believe that there is appreciable mold behind wall cavities, physical inspections should be performed by opening up the hidden area.
Air sampling is appropriate either during or following the inspection. The main purpose of such sampling is to identify contamination that would not be visible without destructive testing and to document air contamination. Air samples should be taken during normal activity in the building, while the ventilation system is operational. They should be collected simultaneously inside and outside the building to enable indoor-outdoor comparisons. The basis of the current methods for interpreting the results of air sampling is a comparison of the diversity of the fungi inside with outdoor air samples.
Sticky surface samplers are increasingly used in mold investigations. Advantages of data from properly collected and analyzed sticky surface samples are twofold: the results are available within a day and in situations when there is a high percentage of non-viable spores in the air, the data are more reliable.
Once the investigation is completed, fungal damage should be expeditiously remediated using state-of-the-art protocols such as those developed by the New York City Department of Health and the ACGIH. As well, quality assurance should be carried out according to standard protocols such as those of the AIHA.
Communication with buildings managers and occupants should be maintained throughout the investigation.
In 1993, the Federal-Provincial Advisory Committee on Environmental and Occupational Health (CEOH) released Indoor air quality in office buildings: a technical guide. This report provided guidance on methods for investigating buildings for air quality problems, including molds. A subsequent report from the same committee, Fungal Contamination in Public Buildings: A Guide to Recognition and Management (1995), provided information on health implications of molds in buildings and a step-by-step protocol for the investigation and interpretation of indoor fungal contamination.
The purpose of this current document is to update the Fungal Contamination in Public Buildings report in view of the large amount of research reported since 1995 on health effects of mold damage in the built environment, as well as on methods for investigating buildings for such damage. This report is not, therefore, intended to replace the Technical Guide, but to provide additional information to those responsible for the investigation and management of fungal contamination in office buildings, schools and other non-industrial workplaces.
Consistent with the 1995 report, this updated review of health effects indicates that living or working in a building with material mold damage is harmful to health. Therefore, indoor mold growth in buildings should be prevented by appropriate control of moisture sources and by timely remediation of water damages. Mold growing in buildings should also be removed under safe conditions using established remediation protocols.
A significant difference between the two documents is the greater emphasis on the general principles of investigation in the current report. As new building investigation techniques become validated, the general principles described here can be used as a framework for their application.
Photo: Canada Mortgage and Housing Corporation (CMHC)
The potential impacts of indoor air contamination on human health have received considerable public attention in recent years. This is especially true in Canada, and other countries with cold weather, where people spend most of their time indoors. Indoor air can be contaminated by pollutants released from carpets and building materials, cleaning chemicals, tobacco smoke, cooking and heating, as well as biological contaminants such as dust mite and animal allergens (derived from skin, saliva and urine) and molds. This report discusses only one aspect of this complex array of contaminants: mold. Much of what is known about the population health effects of biological contaminants in indoor environments comes from studies of people living in damp homes.
Living in damp houses is associated with increased rates of disease, and the cause is believed to be exposure to biological contaminants (Institute of Medicine 2000). Occupants in houses that have dampness problems are at greater risk of exposure to mold, dust mites and bacterial endotoxins. Lower socio-economic status has been associated with higher prevalence of respiratory disease (Dales et al. 2002). In most countries, poverty translates into living in substandard housing that leaks water and air, and is difficult to heat. When houses are difficult or expensive to heat or cool, the air in some rooms is often not conditioned. This leads to moisture accumulation (condensation) on cold surfaces. Depending on the surfaces and degree of house cleaning, contaminants accumulate and airborne particulate concentrations will vary accordingly. Due to complex exposures, however, the attributable risk to each of the biological contaminants discussed here remains unknown. This alone makes it difficult to assign tolerable exposure values.
In addition, outdoor-source fine particles (PM2.5) can be higher indoors than outdoors. Houses near sources of outdoor air pollution (e.g. vehicular traffic) are at greater risk of increased indoor concentrations of particulate matter and volatile organic compounds (VOCs).
Among indoor air contaminants, mold is a cause of increasing concern, with many epidemiological studies and case reports linking mold to a wide range of adverse effects on respiratory health.
The fungus kingdom consists of eukaryotic organisms. Fungi are subdivided into four different phyla based on their reproduction mode: ascomycetes, basidiomycetes, zygomycetes and mitosporic fungi.
The word "mold" is a non-scientific term that in popular parlance generally refers to members of a few dozen filamentous fungi. Such fungi are often visible as colonies on food and building materials, appearing on close inspection as multicellular filaments called hyphae. Mold growth on building material surfaces can influence air quality because both spores and mycelial fragments are dispersed into the air and can be inhaled, depending on their size.
The spores of fungi have a large size range: 1 to 50 µm. Furthermore, the degree of hydration of spores, a consequence of the prevailing relative humidity, affects this range (Madelin and Johnson 1992). Particles at the lower end of the size range (less than 10 µm) can reach the alveoli; others may be swallowed. There is some variation with age: lower airway deposition for 5 µm particles is six times higher in newborns than in adults (Phalen and Oldham 2001). The average aerodynamic diameter of a number of spore types is listed in Table 1. The average sizes of some spores are well within the respirable range (<10 µm); others such as Stachybotrys chartarum appear to be too large to penetrate into the lungs. However, there is considerable variation not represented by the average. For example, even though the average aerodynamic diameter of Stachybotrys spores is too large to penetrate into the lungs, approximately one third of the spores are within the respirable range (Sorenson et al. 1996). Similar data for some strains of Cladosporium cladosporioides, Penicillium viridicatum and P. chrysogenum showed a large range in spore sizes whereas most spores of P. commune, Aspergillus versicolor, A. ustus, A. niger and A. sydowii were of similar dimensions (Miller and Young 1997). As noted, mycelial fragments are also typically present in indoor air. These are usually of respirable size. The number of fragments compared to the number of spores present is highly variable, but typically represent a few percent of the fungal particles present. It is known that mycelial fragments of some species contain different allergens than those present in spores of the same species (Górny et al. 2002).
|Cladosporium cladosporioides||2.3||(2.0-3.5) x (2.0-2.5)|
|Paecilomyces variotii||2.7||2.9 x 1.3|
|Penicillium chrysogenum||2.6||2.5 x 2.5|
(After Madelin and Johnson 1992; Sorenson et al. 1996).
Three features of mold biochemistry are of special interest in terms of human health. First, mold cell wall contains (1->3)-ß-D-glucan, a compound with inflammatory properties. Second, spores and mycelial fragments contain allergens (Górny et al. 2002), few of which have been chemically characterized. Many of the known fungal allergens are serine proteases, or proteins, which are present in fairly high concentrations in the spores. These have been described mainly from work done in phylloplane species and Aspergillus fumigatus (Horner et al. 1995). Third, the spores of some species contain low molecular weight chemicals that are cytotoxic or have other toxic properties (e.g. satratoxins produced by Stachybotrys chartarum). Some molds, such as Aspergillus fumigatus, can cause opportunistic infection in immunocompromised individuals and severe allergic diseases in people with underlying respiratory conditions, such as asthma or cystic fibrosis (Burge 2000).Fungi commonly found in moldy building materials are shown in
Table 2. Common fungi from mold-damaged building materials
Photos : Centraalbureau voor Schimmelcultures, Koninklijke Nederlandse Akademie van Wetenschappen, Pays-Bas
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.
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.
Cross-sectional studies are studies in which outcomes (diseases) and exposures are assessed at one point of time. Eight cross-sectional studies, summarized in Table 3, investigated the relationship between indoor mold and respiratory, allergic or irritation symptoms, and four found significant association between mold exposure and either physician-diagnosed asthma or asthma-related symptoms (cough, wheezing or breathlessness).
Table 3. Cross-sectional studies on respiratory and allergic effects of exposure to indoor molds, 1995 to 2001
In case-control studies, exposure is assessed and compared between subjects with the disease of interest (cases), and without this disease (controls). Nine case-control studies, summarized in Table 4, have investigated the relationship between mold and asthma, most of them relying only on self-reports to assess both mold exposure and health outcomes. One of these studies found a significant association between "mold or dampness" and asthma; another found a significant association between mold and asthma, but did not assess dampness; three found significant associations between mold and asthma (one of them after controlling for dampness), but not between dampness and asthma, and two found significant associations between dampness and asthma, but not between mold and asthma. Interestingly, these two studies used objective criteria rather than self-reports to assess health outcomes, and home inspection for assessing exposure or validating the exposure questionnaire.
Sick building syndrome (SBS) describes a series of symptoms with no clear etiology, such as eye, nose and throat irritation, headaches and high frequency of airway infection and cough, which are associated with a building environment. It is distinguished from building-related illnesses (BRI) which are well-defined responses to biological, physical or chemical exposures occurring in indoor environments (Brightman and Moss 2000). SBS and BRI investigations were mostly cross-sectional (i.e. comparing occupants of buildings where problems were identified to those of "control" buildings). Some of these studies included a longitudinal component, as the health of exposed individuals was reassessed after exposure had been eliminated.
Some of these studies where mold contamination was investigated, along with other exposures, are summarized here. It should be kept in mind that because of their cross-sectional design and some other methodological issues (multiple concomitant exposures, possible bias in studies initiated following complaints), these studies cannot identify or demonstrate an independent association between an exposure such as mold and dampness, and a health outcome.
In cohort studies, subjects classified according to their exposure are followed over time to determine the incidence of the disease of interest. To date, no cohort studies have been published on the association between residental mold exposure and asthma, although a published study has investigated the association between mold exposure at school and childhood asthma (see below). In addition, there is an ongoing cohort study in Prince Edward Island, Canada.
In Sweden, a prospective study was carried out over four years; a total of 1,347 children was surveyed twice, in 1993 and in 1997. Their mean age in 1993 was 10.3 years. Participants were attending 39 different schools at the time of the first survey. Total mold concentrations were determined in 1993 and 1995 and ranged from 5 to 360 cells/m3 (arithmetic mean 26 cells/m3). After adjustment for sex, age, atopy in 1993, and smoking, the odds ratios for incident asthma (i.e. diagnosed during the follow-up period) per 10-fold increase in total mold levels in classrooms was 1.3 (95% CI 0.5 to 3.6). Among children who were not atopic in 1993, the odds ratio for incident asthma per 10- fold increase in mold levels, adjusted for sex, age and smoking, was 4.7 (95% CI 1.2 to 18.4) (Smedje and Norbäck 2001).
Some sub-populations have been found to be at increased risk of developing rare conditions following exposure to molds. Exposure to extremely high mold contamination has been associated with pulmonary hemorrhages in infants, and increased risk of invasive mycose has been observed in people with immune suppression.
Exposure to indoor molds has been a suspected cause of idiopathic pulmonary hemorrhage in infants and young children. In most cases, the suspected etiologic agent was Stachybotrys chartarum (also known as S. atra), a hydrophilic fungus (i.e. requiring very damp conditions to grow) that produces cellulase and is therefore able to use cellulose as a substrate. Stachybotrys chartarum produces at least four families of compounds: atranones, macrocyclic trichothecenes, spirolactones and cyclosporin-like compounds (Sakamoto et al. 1993; Jarvis et al. 1995; Hinkley et al. 1999). There appear to be two chemotypes present in North American strains: those that produce all of the families of compounds and those that do not produce tricho-thecenes, but do produce the others. Both types appear to occur together (Nielsen et al. 2002).
In Cleveland, Ohio, 10 infants aged less than one year were diagnosed with pulmonary hemorrhages and hemosiderosis between January 1993 and December 1994. Each of these cases was matched for age with three controls. Data collection was performed by a questionnaire administered to parents and sampling of molds on surfaces and in the air. Mean concentrations of viable mold conidia in the air were higher in houses of cases compared to houses of controls (total viable fungi: 29,227 CFU/m3 vs. 707 CFU/m3; Stachybotrys chartarum: 43 CFU/m3 vs. 4 CFU/m3). A 10-CFU/m3 increase in the concentration of viable Stachybotrys chartarum conidia was associated with a significantly increased risk of acute pulmonary hemorrhage (OR 9.83, 95% CI 1.08 3×106). Nine out of 10 cases lived with smokers, compared to 16 out of 30 controls (OR 7.9, 95% CI 0.9 to 70.6), suggesting that exposure to environmental tobacco smoke may act synergistically with the factors associated with damp buildings (Montaña et al. 1997; Etzel et al. 1998). A review panel mandated by the US Centers for Disease Control and Prevention (CDC) to reassess this investigation concluded that the methodology used to collect mold samples and to calculate airborne counts of viable spores was inappropriate (CDC 2000).
No other published epidemiologic study has investigated the association between exposure to S. chartarum and pulmonary hemorrhage, but cases of pulmonary hemorrhage have been reported in infants and young children exposed to it (Elidemir et al. 1999; Flappan et al. 1999) or to other hydrophilic, cellulolytic fungi (Novotny and Dixit 2000). In the Cleveland hospital where the initial outbreak occurred, 30 infants were hospitalized with acute pulmonary hemorrhage between 1993 and 2002. Twenty-six out of 29 infants lived in water-damaged buildings, and 25 out of 28 in homes containing toxigenic fungi (Dearborn et al. 2002).
In 2000, the CDC created three new working groups to develop better protocols for investigation of future clusters. Briefly, a review of patient records from the Cleveland cases by pediatric and other specialists indicated that there were no known potential causes for the disease reported in the original studies. A clear case definition was developed should any additional clusters of infant pulmonary hemorrhage be detected. Most of the babies included in the original studies and subsequent infants studied would be included by the new definition (Dearborn et al. 2002). A second working group concluded that the fungal exposure assessments in the original study were inadequate. Several investigation techniques were described in case of future reports of clusters of idiopathic pulmonary hemorrhage. Some of these techniques would not have been available at the time of the original investigation (CDC 2001). A third group devel oped a protocol for surveillance and CDC has begun a surveillance program in conjunction with the states (CDC 2004).
Some fungi such as Aspergillus species are ubiquitous in the environment, and inhalation of their spores is very common. However, invasive mycoses (i.e. fungal infections) occur mostly in immunosuppressed patients. The most common pathogen is Aspergillus fumigatus (Bennett 1994). The incidence of invasive mycosis is increased in AIDS patients; an analysis of medical records of 35,232 HIV-infected patients who attended outpatients clinics in 10 US cities between 1990 and 1998 revealed that the incidence of invasive aspergillosis was 5.1 per 1000 (95% CI 2.8 to 7.3) in those with CD4 counts 50 to 99 cells/mm3 and 10.2 per 1000 in those with CD4 counts lower than 50 cells/mm3, compared to 1.0 per 1000 (95% CI 0.6 to 1.4) in those with CD4 counts equal to or higher than 200 cells/mm3 (Holding et al. 2000).
Some fungi such as Aspergillus species are ubiquitous in the environment, and inhalation of their spores is very common. However, invasive mycoses (i.e. fungal infections) occur mostly in immunosuppressed patients. The most common pathogen is Aspergillus fumigatus (Bennett 1994). The incidence of invasive mycosis is increased in AIDS patients; an analysis of medical records of 35,232 HIV- infected patients who attended outpatients clinics in 10 US cities between 1990 and 1998 revealed that the incidence of invasive aspergillosis was 5.1 per 1000 (95% CI 2.8 to 7.3) in those with CD4 counts 50 to 99 cells/mm3 and 10.2 per 1000 in those with CD4 counts lower than 50 cells/mm3, compared to 1.0 per 1000 (95% CI 0.6 to 1.4) in those with CD4 counts equal to or higher than 200 cells/mm3 (Holding et al. 2000).
Several outbreaks of invasive aspergillosis have been reported in hematology wards where neutropenic leukemia patients were housed. The risk of invasive aspergillosis in immunosuppressed patients was associated with the airborne concentrations of Aspergillus spores, and increased incidences have been observed following events resulting in higher Aspergillus counts in the air, such as construction or dysfunction in air filtration systems.
Community-acquired (i.e. out of hospital) opportunistic invasive aspergillosis is not as well documented, but some cases have been reported (Benoit et al. 2000; Chen et al. 2001). Immunosuppressed patients remain vulnerable to Aspergillus infections if exposed in the outpatient setting or at home after being released from hospital (VandenBergh et al. 1999)
Fungi can colonize the lungs or nasal cavity of patients with underlying respiratory disease such as asthma or chronic rhinosinusitis. This condition is referred to as allergic bronchopulmonary mycosis when occurring in the lungs, and as allergic fungal sinusitis when taking place in the nasal cavity. Since Aspergillus species (especially Aspergillus fumigatus) are the most common etiologic agents causing allergic bronchopulmonary mycosis, this condition is commonly referred as allergic bronchopulmonary aspergillosis, or ABPA. Both conditions are characterized by eosinophilia and by the presence of non-invasive fungal hyphae in sputum or in nasal mucus (Hunninghake and Richerson 1994; Ponikau et al. 1999). Case reports have suggested a link between fungal counts in the air and the development of acute bronchopulmonary mycoses (Beaumont et al. 1984; Kramer et al. 1989; Ogawa et al. 1997).
Several experimental studies with animal models exposed to fungal cells, antigens or constituents have found effects similar to those observed in humans in epidemiological studies, such as eosinophilia and increased serum IgE.
Also, some studies found severe hemorrhagic responses induced by Stachybotrys chartarum spores.
Other studies with rodents exposed to Stachybotrys chartarum showed effects on lung physiology that may be mediated by different mechanisms.
The major findings on the health effects of mold can be summarized as follows.
In most epidemiological studies on indoor mold and health, the exposure assessment was based on participants' self-reports. In the few studies where exposure to mold was assessed by a member of the research team, the exposure classification was based on dichotomous questions such as the presence or absence of dampness and/or mold; there was no quantitative exposure assessment, and therefore no determination of a dose-response relationship. Exceptions are the studies of Garrett et al. (1998) and Dales et al. (1999). Also, in most cross-sectional and case-control studies, the mold taxa present in homes were not identified. Mold species differ considerably, not only in their potential to cause adverse effects to human health, but also in the mechanisms by which they can affect health (i.e. through releasing volatile compounds, aller gens or mycotoxins) and, therefore, in the nature of effects they can cause.
The difficulty of quantifying human exposure to mold is thus a major obstacle in ascertaining the existence of cause-and-effect relationships, as dose-response relationships cannot be assessed. This difficulty has led the Institute of Medicine (2000) to conclude that ". . . standardized methods for assessing exposure to fungal allergens are essential, preferably based on measurement of allergens rather than culturable or countable fungi . . ." in order to obtain a clear understanding of the effects of building-related fungi.
Quantitative measurement, rather than questionnaire-based assessment, of exposure to fungi may be a promising way to improve epidemiological studies. However, the traditional method of exposure measurement (i.e. air sampling and culture of fungal spores) shows several limitations that make their utility questionable. For example, airborne fungal spores can be sampled only over short periods of time, while air counts of fungal spores vary considerably over longer periods of time. Also, the culture medium used always favours some species over others, and some fungal taxa have the ability to inhibit the growth of other taxa in culture media.
For all the reasons mentioned above, the determination of surrogate markers of fungal growth, such as ergosterol and (1->3)-ß-D-glucan, in house dust appear to be more promising (Dillon et al. 1999). Both ergosterol and (1->3)-ß-D-glucan are cell membrane constituents in fungi (Li and Hsu 1996; Miller and Young 1997). (1->3)-ß-D-glucan has been associated with increased peak expiratory flow (PEF) variability in asthmatic children (Douwes et al. 2000). There is, however, a need for further research to develop standardized protocols for the determination of (1->3)-ß-D-glucan in the environment (Dillon et al. 1999). Determination of extracellular polysaccharides (EPS) of Aspergillus and Penicillium in house dust is another approach being developed for the assessment of exposure to mold. EPS is a fungi-specific marker but, unlike glucan, it is not suspected to be causally related to adverse effects on respiratory health (Chew et al. 2001).
Molecular approaches have been developed for assessing both qualitative and quantitative fungal exposure in buildings and other environments (Haugland et al. 1999). To date, there is little practical experience with this approach. Some research groups have proposed using animal-derived antibodies to provide quantitative and qualitative information on fungal exposure (Wijnands et al. 2000a, 2000b). Another approach to measuring fungal exposure, advocated by the US Institute of Medicine Committee on Asthma (Institute of Medicine 2000), is to determine human fungal allergens or antigens. Research is under way on this in Canada.
Objective assessment of health outcomes is another weakness of many epidemiological studies on health effects of mold exposure, since most studies rely on subjective assessments by questionnaires, which once again render the drawing of firm conclusions more difficult. Objective measures of health outcomes do exist, but incorporating them into studies greatly increases study costs.
Damp conditions favourable to mold growth are also favourable to other biological agents known to be allergenic, such as dust mites and gram-negative bacteria.
Unlike mold, bacteria are not visible and, therefore, their presence can be assessed only by air or dust sampling. Therefore, the association observed between mold exposure and allergic responses could be explained in part by confounding bacteria or dust mites being associated with both the exposure to mold and the outcomes considered. This may explain the findings, in some studies (Williamson et al. 1997; Norbäck et al. 1999), of stronger associations between dampness and asthma than between visible mold and asthma. However, in a cross-sectional study where bacterial endotoxins and dust mites were actually measured, controlling for these other allergen levels did not affect the association between indoor mold and respiratory symptoms (Dales and Miller 1999). Moreover, a case-control study revealed a significant association between mold growth and asthma after controlling for visible dampness (Thorn et al. 2001). Also, experiments in animal models showed that mold antigens are able to induce allergic responses in the absence of endotoxin or other biological agents (Alonso et al. 1997, 1998; Cooley et al. 2000).
Chemical exposures may also be confounders in at least one of the studies summarized above. In Smedje and Norbäck's (2001) cohort study, both airborne fungi and formaldehyde were significant risk factors for incident asthma, but could not be included together in multivariate models because of their strong mutual association.
Other potential confounders in respiratory disease epidemiology, such as socio-economic status, smoking and environmental tobacco smoke exposure, have been controlled for in the majority of cross-sectional and case-control studies reviewed, and are therefore unlikely to explain the findings.
There may be a reporting bias in some studies, as there is an increasing awareness in the population that molds are suspected to cause respiratory health effects. People with mold problems may pay more attention to symptoms experienced by their children or themselves. This is likely to have occurred in the Finnish cross-sectional study that found an association between mold and backaches and stomachaches (Pirhonen et al. 1996). As well, people with respiratory health problems may pay more attention to the presence of mold, as physicians investigating asthma or other respiratory diseases commonly ask patients if they have been exposed to mold or dampness, but this bias was eliminated in many studies by having houses inspected by an investigator blind of participants' case or control status. In the Williamson et al. (1997) case-control study, where the possibility of such a bias was reduced by a case or control classification based on hospital records and exposure assessment based on home visits, an odds ratio of 1.7 (but non-significant) was found between severe dampness and asthma.
To our knowledge, only one cohort study was published on health effects of indoor, non-occupational exposure to molds (Smedje and Norbäck 2001). At the time of writing, another cohort study is being conducted in Canada, the Prince Edward Island infant health study. The evidence linking mold to health effects arises mostly from cross-sectional and case-control studies. These two designs are generally considered weaker than cohort studies for investigating the etiology of disease, since it is difficult to ascertain that the suspected cause actually preceded the disease under study. However, though asthma and allergy are chronic conditions, asthma symptoms can improve when exposure to allergens and/or irritants that induce broncho- constriction is removed. A cross sectional or case-control study finding an association between "mold and/or dampness" and chronic wheezing does not demonstrate that mold has caused the onset of asthma, but it may indicate that either mold or dampness induces respiratory symptoms in asthmatics (assuming, of course, that both exposure and outcome assessments are accurate; see previous sections). On the other hand, cohort studies of home indoor environments and respiratory/allergic diseases (preferably with objective assessment of exposure and outcome, such as home inspection and physical assessments) are needed to ascertain the existence of a causal link between mold and respiratory diseases.
As seen in section 2.4.1, several studies have found significant associations between exposure to mold and/or dampness, and irritative and non-specific respiratory symptoms, as well as the exacerbation and development of respiratory diseases such as asthma. Due to limitations in the assessment of both exposure and outcomes, and since in almost all studies to date an independent effect of mold could not be isolated from that of other contaminants associated with dampness, epidemiologic data alone are insufficient to conclude that indoor mold causes respiratory disease. However, such a causal link is highly plausible in view of the fact that exposure to fungi in occupational environments causes allergic and toxic disease and that adverse effects of fungi have also been seen in inhalation studies using animal models.
In the hospital setting, airborne exposure to certain fungi is associated with an increased risk of fungal infection in immunocompromised individuals.
Although further investigation of health effects of indoor fungi by means of improved exposure and health outcome assessment methods are needed to resolve uncertainties, current knowledge supports the need to prevent damp conditions and mold growth and to remediate any fungal contamination in buildings.
Photo: Architectural Diagnostics Ltd.
A safe workplace is mandated by law in Canada under various legislative frameworks. These include Section 12 of the Hazardous Products Act1, the Canada Labour Code, the Transportation of Dangerous Goods Act, provincial occupational health and safety acts, and related regulations. It is essential to have in place an operating procedure that will protect the health and safety of occupants2, as well as the workers performing their duties in the investigation of possible fungal contamination in public buildings3 (CEOH 1995a). Analyses of the legislative framework for indoor air quality (IAG) in Canada illustrated its variable nature and described the case law that might apply (Beaudry 1999; Morton and Kassirer 2000).
Recent reviews indicated that there is no specific regulatory mention of most contaminants present in residential or office indoor air (CEOH 1989, 1995). As is the case with other indoor air contaminants, the legal framework for mold is mainly based on regulations that suggest or require the adherence to the advice of cognizant authori ties, including CEOH, the American Society of Heating Air-Conditioning & Refrigerating Engineers Standard 62, and the ACGIH Threshold Limit Values (TLVs), as well as determinations or policies of provincial and territorial labour and health departments. In addition, health and safety requirements in legislation impose some obligations to industrial hygienists, professional engineers, physicians and other health professionals to act in accordance with the best interests of occupants. This should be done in accordance with the policies of the designated Medical Officer of Health or Public Health Directors for the area concerned and/or Health Canada for federal jurisdictions.
It cannot be emphasized enough that the best way to manage mold growth is to prevent it before it occurs. The essential elements of a prevention strategy are the control of moisture, the timely remediation of any water leakage, and adequate maintenance of heating, ventilation and air conditioning (HVAC) systems (Lavoie and Lazure 1994; Flannigan and Morey 1996).
Indoor air quality investigations4 can begin in several ways. Some building owners or managers conduct regular air quality audits to detect problems before they can potentially affect occupants. At the other end of the spectrum are investigations which occur as a result of acute reactions from individuals entering a building. Appropriate measures should be taken when an investigation is prompted by health complaints. It is important to involve specialists with recognized professional training and experience to investigate potential mold problems in public buildings using methods documented by the ACGIH (1999) and the American Industrial Hygiene Association, or AIHA (Dillon et al. 1996).
In HVAC systems, humidifiers, dirty filters and accumulated debris in ducts subject to condensation or leaks can all be sources of building-associated mold. Spores can be blown out of ducts in a periodic fashion. Fungi can be released when occupied spaces adjacent to contaminated wall cavities, elevator shafts or faulty sewer drains are depressurized. Release from these sources can be affected by air infiltration rates and pressure differentials resulting from wind and thermal loading (weather) and unbalanced ventilation or exhaust systems. Distribution of fungi from carpets or surface contamination is affected by activity in the occupied space and the intensity of cleaning.
If required, laboratory tests must be done using appropriate methods and by qualified and experienced professionals. Commercial laboratories should demonstrate successful performance in the AIHA Environmental Microbiology Proficiency Analytical Testing (EMPAT) program and preferably be an Environmental Laboratory accredited by the Standards Council of Canada (SCC),5 or ISO or Good Laboratory Practice (GLP) certification.6
There are also university and governmental laboratories with highly qualified specialists in mold identification that can provide reliable data; however, they must be required to use recognized methods. Canada Mortgage and Housing Corporation (CMHC) attempts to maintain a list of laboratories that have provided services for the Government of Canada. Provincial officials in Health or Labour Departments may also be able to provide recommendations. All reasonable steps must be taken to ensure that no action during the investigation or remediation7 process results in further contamination of the building or increased risk for occupants or the public. Finally, the provision of reliable and timely information to occupants is a critical aspect of any IAQ investigation because of the need for individuals in one of the potential risk groups to be informed in the event of a microbiological problem in their workplace or education facility.
As noted above, the intensity and complexity of mold investigations vary according to the size and nature of the building, whether an air quality audit is being conducted or whether the investigation is a response to a health complaint. The benchmark is the CEOH (CEOH 1989, 1995a, 1995b) advice to minimize exposure to fungi, that there are population health effects of mold and dampness and that there are risk groups. The goals are to define and manage the microbial problem(s) and return the building to a satisfactory level of performance. Air quality investigations for audit purposes are not considered here.
The following discussion refers to an incident in which a health complaint has been made and initial evidence shows that mold might be one of the potential issues.
The goals of such investigations are to:
Factors to consider when addressing a potential mold problem
5. The Standards Council of Canada (SCC) offers environmental laboratory accreditation in partnership with the Canadian Association for Environmental Analytical Laboratories (Inc.) (CAEAL). CAEAL is a not-for-profit association of public and private sector laboratories.
6. Good Laboratory Practice (GLP) refers to compliance with a series of guidelines, developed by the Organisation for Economic Co-Operation and Development (OCED), regarding laboratory facilities, standard operating procedures (SOPs), quality assurance and reporting. GLP certication is granted by a number of agencies around the world, including the US Food and Drug Administration.
7. "Remediation" includes both the thorough cleaning of any mold growing in the building and correcting the building defect that led to mold growth (excessive humidity, water leaking, or water infiltration from the outside).
8. Residual dust should be reduced to as low as can reasonably be achieved. This has been defined as less than 100 mg dry weight/m2 on smooth surfaces in a number of cognizant authority documents (ACGIH 1999; AIHA 2001).
Microbiological sampling during a building investigation for mold-related problems is complicated. Several cognizant authorities have published guidance on this topic. For example, the AIHA published a Field Guide of consensus methods for microbiological sampling (Dillon et al. 1996). The ACGIH has published a comprehensive manual on microbiological problems of buildings, including chapters on investigation and remediation that recognize the AIHA manual as a source for sampling methods (ACGIH 1999). Details on some of the procedures can also be found in Flannigan, Samson and Miller (Flannigan et al. 2001). The US Environmental Protection Agency (EPA) has also published mold remediation guidance for public buildings (USEPA 2001) and for homes (USEPA 2002).
The goals of any investigation are to establish the cause, nature and extent of fungal contamination and to assess the risk of adverse effects on the health of occupants.
The first step in investigating a building for microbial contaminants is an informed inspection. This should be performed by someone with engineering or architectural knowledge of moisture problems in buildings, considering the type of building under investigation. The investigation of large public buildings requires a different skill set than a house. Mold contamination can arise from condensation, floods and various types of leaks. Inspection of mold problems requires a thorough knowledge of the design of the building envelope and of the types of failures that result in condensation and water leaks. The physical investigation of molds in both public and domestic buildings requires considerable expertise in the design, construction and operation of these structures. Informed inspection checklists suitable for residential housing have been developed by CMHC (1993) and by Public Works and Government Services Canada (Davidge et al. 1992) and the USEPA (USEPA and USDHHS 1991) for public buildings.
Air sampling is not appropriate unless a thorough building inspection is done either on a concurrent basis or before sampling. Sampling is done to identify contamination that is not visible without destructive testing and to document air contamination. Similarly, after sample results are obtained, the data must be compared with the information obtained during the physical inspections. "Are the results plausible?" is a question that must always be asked and answered to properly assess the risk of false negative and false positive results for mold contamination. Additionally, documentation of the sources and nature of the contamination allows a failure analysis to be done on the building (or HVAC system). This will assist in developing cost-effective investigation strategies and ultimately any remedial action necessary.
Air samplers collect fungal propagules either on agar media or in aqueous suspensions. Such samples provide information on culturable or "viable" propagules in air. It is important to consider that existing air-sampling techniques underestimate the true airborne concentrations of fungal spores for several reasons. The number of fungal propagules determined by culture are substantially less (by 1% to 50%) than those determined by direct methods; however, this varies between species. Different species of fungi have different growth requirements so the use of any medium produces different recoveries. The spores of fungi decline in viability with time; the spores of some species remain viable for years and for other species for months. Some species grow very fast or are aggressive in culture and produce antifungal agents that can affect the growth of other species present in culture. The variability of spore clouds in the air in a building with active mold growth is much larger than the precision of available sampling methods. Air sampling is useful for investigating large buildings for mold contamination and must be considered if the investigation was prompted by health complaints.
It is seldom possible to take enough samples to conduct rigorous statistical analyses, but statistical principles need to be considered when determining the number of samples to be taken (ACGIH 1999). Careful consideration must be given as to how and where each sample is to be taken.
Air samples should be taken during normal activity in the building, while the ventilation system is operational. Factors to consider include taking samples in a given space and allowing one or two hours between duplicates (e.g. go around each floor of the building in one direction, go up each level and then down, morning and afternoon, etc.). This technique takes into consideration the variability of airborne spore concentrations over time and with different activities, as well as varying thermal and wind loads. Air samples should not be taken when it is raining. Rain has a transient effect on the microbial populations in outdoor air that can result in a reduction of the sensitivity of the indoor-outdoor comparison. The number of outdoor air samples should in principle be equal to the num ber taken indoors. Since this is seldom practical, there needs to be at least between three and six samples taken outdoors during the period(s) when the indoor sampling is under way. These need to be taken above grade to avoid collecting windblown soil particles containing fungi which can affect the comparison of the indoor-outdoor diversity. It is recommended that outdoor air samples be collected as close to the air intake as possible or facing into the wind on the building roof. Other considerations can be found in the AIHA Field Guide (Dillon et al. 1996) and the ACGIH bioaerosols manual (ACGIH 1999).
The basis of the current methods for interpreting the results of air sampling is a comparison of the diversity of the fungi inside with outdoor air samples, taking into account indicator species and species with poor recoveries on agar media such as Stachybotrys chartarum (CEOH 1995a; Dillon et al. 1996; ACGIH 1999). There is a shifting array of fungal species in outdoor air as the season progresses. Average numbers of total propagules in July range from 20,000 per m3. to peak levels of twice that value. In the absence of snow cover, total Aspergillus/ Penicillium comprise <1% of the total fungal spores present in outdoor air. When there is snow cover, the total number of fungal spores decreases, and the proportion of Aspergillus/Penicillium therefore increases to 10% to 20%.
The advantage of properly collected and analyzed viable air samples is that the data can be used to detect signs of the early stages of a mold problem, as well as growths in wall cavities or ventilation ducts (where dilution by outside air limits the sensitivity of the analysis).
Sticky surface samplers such as Zefon Air-O-CellTM, AllergencoTM and BurkhardTM are increasingly used in IAG investigations. There is little published information on their comparative quantitative and qualitative performance (Dillon et al. 1996). However, some studies have provided information on the cut points of these samplers (Aizenberg et al. 2000). A limitation of these methods is the skill of the microscopist in counting fungal propagules in a field containing debris of various kinds.
Advantages of data from properly collected and analyzed sticky surface samples include the fact that the results are available within a day and in situations when there is a high percentage of non-viable spores in the air, the data are more reliable.
Within the informed inspection component of the overall investigation, detailed notes of the amounts of mold visible should be noted on the appropriate perspective of the building plans. The moldy areas should be drawn on the plan with sufficient accuracy to permit an estimation of the number of square metres of mold.
Bulk samples might be collected from the visibly moldy building materials to delimit the affected areas by examining the materials for fungal growth. A small amount of material can be scraped off the surface and examined under the microscope and/or plated on agar media. Usually, the colour of visibly moldy material comes from conidia, ascocarps, pycnidia and, in the case of melanized fungi, the mycelia. Conidia that are not visible to the naked eye, but present on building materials may still have the potential to affect the air quality of the occupied space.
Where there is probable cause to believe that there is appreciable mold behind wall cavities, physical inspections should be performed by opening up the hidden area. Factors to consider include whether there is insulation in the walls and what kind of water damage has occurred. For example, if there has been a pipe burst, flood, fire storm or evident problems with the cladding or windows, all affected areas can be reasonably suspected of having been affected and need to be examined for mold damage. The informed inspection and/or air samples can be useful in determining whether destructive testing is required. Methods range from sawing the bottom 0.3 metre off one side of interior walls to using a keyhole saw and a boroscope (AIHA 2001). Such destructive testing should be done with source control HEPA vacuums (e.g. near the saw) or under simple containment, using all appropriate respiratory protection required (ACGIH 1999).
Bulk samples refer to physical, destructive samples of building materials. Dilution plating methods are selective and do not provide direct information on the fungi growing on the damaged material versus dormant organisms that might have settled out from the air. Dilution plating involves taking an amount of a powered material (e.g. ground wallboard, settled dust) and suspending it in an appropriate diluent. This is then further diluted in 10-fold steps and aliquots are plated on agar media at least in triplicate, followed by spreading the liquid evenly over the surface, incubating and counting the colonies that emerge. Representative colonies are then transferred to agar media appropriate to identify the species present. The strength of this method is that a picture of the diversity of species present can be obtained.
In the absence of regular HEPA vacuum cleaning, mycological analysis of settled dust samples has value in identifying a problem that might be seasonal or due to factors not present at the time of the investigation (ACGIH 1999). For example, condensation around perimeter induction units, which leads to wet carpets, occurs only in the summer. Investigation of occupant complaints may occur when the carpet is not wet. As is the case for air samples, interpretation of dust samples is appropriately made by analysis of the fungal diversity, but is less straightforward (Dillon et al. 1996; ACGIH 1999).
Small pieces of building materials collected (ca. 0.5 g) can be plated on different agar media. These are incubated and the colonies that grow out are counted and transferred for identification. The advantage of this method is that the colonies that first emerge from moldy building material are likely to be the most reflective of those active in the damaged material.
Samples of moldy building materials that are plated by either method should also always be mounted in lactophenol cotton blue or other appropriate stain and examined by microscopy to determine the presence of organisms that might not be viable. This allows a comparison to be made between viable and non-viable cultures. This will provide information on the dead fungi present on damaged material to be obtained, thus helping prevent false negative results. (Dead fungal spores still contain allergens and toxins.) If the majority of the fungi are found to be dead on a moldy item, the water event probably occurred months to years ago.
There are two basic techniques to examine moldy surfaces by microscopy: tape samples and mounting scrapings of the mold-damaged area collected in small plastic bags or vials. Tape samples are made by pressing the affected surface with good quality cellophane tape. If scrapings are available, they can be mounted on slides and examined; they can also be cultured whereas the tape samples cannot. As with all microscopic methods, large dark spores are easier to see and, depending on the skill of the microscopist, small hyaline spores are often overlooked. The taxonomic information obtained is limited.
Some of the following hyperlinks are to sites of organizations or other entities that are not subject to the Official Languages Act. The material found there is therefore in the language(s) used by the sites in question.
The guidance offered above on remediation and inspection emphasizes the need to use investigators who are qualified and experienced in this aspect of engineering and industrial hygiene. Because there is considerable variation in construction methods used and in climates across Canada, such investigations cannot be standardized in detail.
The guidance on mold sampling has emphasized that sampling is often a necessary part of investigation for public buildings and less useful for house dwellings.9 Sampling should be done by qualified and experienced investigators using laboratories with demonstrated proficiency.
As noted in most current documents concerning mold in buildings, prevention is key. Prompt attention to condensation and water leaks in the building fabric, and wet building materials (resulting from plumbing or other causes, such as flood or storm damage) will eliminate the growth of mold and prevent the increase of other contami nants, such as house dust mites in the built environment. Such preventive actions are relatively inexpensive compared to the costs associated with remediation of mold problems in buildings. The value of prevention appears even more obvious when one takes into account health problems that may be avoided.
9 CMHC has posted a discussion of the merits of mold sampling in single family dwellings on its Web site: http://www.cmhc-schl.gc.ca
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