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8 INDOOR DAMPNESS AND As th ma One of the environmental factors most commonly associ- ated with respiratory disease is building dampness. This chapter presents an overview of the research on dampness and human health, and the nature, causes, and control of dampness problems. There is a large and detailed literature addressing the engineer- ing and physics underlying moisture control in buildings (e.g., Trechsel, 1994~. In addition, professional organizations such as the American Society for Testing and Materials and the American So- ciety of Heating, Refrigerating, and Air Conditioning Engineers publish reference materials and promulgate consensus standards intended, in part, to limit indoor moisture problems. A task force formed by the International Society of Indoor Air Quality and Climate published guidelines for the control of moisture-related problems in 1996 (Flannigan and Morey, 1996~. A complete treatment of the science and art of controlling in- door moisture is beyond the scope of this report. As this overview suggests, moisture in buildings is an area of research that has the potential to significantly affect public health. The committee be- lieves that better communication between health, engineering, and building professionals is likely to result in more informed studies on the health effects associated with moisture problems and the means to prevent or remediate these problems. It strongly encourages efforts to bring these groups together to educate one 298

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INDOOR DAMPNESS AND ASTHMA 299 another on their areas of expertise and to establish collaborations aimed at improving the public's health. INDOOR WATER SOURCES AND REMOVAL PROCESSES Water is present in buildings as vapor within the indoor air, as a liquid reservoir, as a solid (ice or frost), as a layer of mol- ecules adsorbed on the surface of building materials, or as con- densation within the pores of these materials. A continuous pro- cess of moisture transfer occurs among the phases and indoor locations of water. The observed relationship of moisture prob- lems to asthma is presumed to be a consequence of the influence of moisture on the growth of microorganisms on building materi- als; consequently, the moisture content of materials is of primary interest for asthma. However, the moisture content of building materials is influenced by the other phases and locations of mois- ture within the building. Sources of water on or within building materials include leaks of liquid water from interior plumbing or from outdoors above or below grade. Other sources include melting of ice or frost (e.g., in attics), capillary transport from moist soil (e.g., through concrete foundations), water vapor condensation, and the water present in building materials (e.g., wood or concrete) at the time of build- ing construction, which is particularly significant during the first year after construction. Additionally, water vapor from air sur- rounding a building material adsorbs on or in building materials. The equilibrium moisture content of a building material sur- rounded by air is primarily a function of the relative humidity of the air; however, the equilibrium relationship varies considerably among building materials (Kumaran et al., 1994~. Sources of water vapor in indoor air include the water vapor in incoming outdoor air, which is often a dominant source during hot humid weather. Air that is drawn into buildings from craw! spaces or after passing through soil and cracks in the building substructure may be particularly humid. Additional indoor wa- ter vapor sources include human respiration; evaporation that occurs from water-using activities such as cooking, bathing, wash- ing, and drying; intentional humidification; evaporation from liq- uid water that originates from leaks or condensation; and the de

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300 CLEARING THE AIR sorption of water from materials. Combustion products that en- ter the indoor air space due to the use of unvented gas or kero- sene heaters or a failure of the venting of "vented" heating equip- ment can be a large source of water vapor. Christian (1994) summarizes information on the rates of water vapor production from many of these sources. Removal processes for indoor water vapor include the flow of air with water vapor from indoors to outdoors (i.e., ventila- tion), absorption on surfaces, the intentional water vapor conden- sation that occurs in air conditioning and dehumidification sys- tems, and unintentional water vapor condensation on surfaces. Water vapor condenses from air when the air temperature is cooled below the dew-point temperature. In buildings, uninten- tional water vapor condensation occurs when humid air contacts coo! surfaces. In winter, the temperature of portions of the build- ing envelope that exchange heat with outdoor air or soil may fall below the dew-point temperature of indoor air, leading to water vapor condensation. The condensation that occurs on windows is a familiar phenomenon; however, condensation can also occur within the building envelope as humid indoor air passes through the envelope and comes in contact with coo! surfaces. In the sum- mer, surface temperatures in air-conditioned buildings may be lower than the dew-point temperature of the outdoor air. Con- densation may occur as the warm humid outdoor air flows into the building and contacts these surfaces. Vapor barriers (i.e., sheets of material with a low permeability to water vapor that also retard air flow) are commonly installed in building envelopes to limit moisture transport and the associated risks of condensa- tion. Vapor barriers should be installed near the warm side of the building envelope for example, near the inner surface of walls in a building located in a cold climate. Improper placement of vapor barriers or unintentional vapor barriers can lead to con- densation. Impermeable viny! wallpaper located on the inner sur iAn estimated 0.5 million unvented gas heaters were sold in 1996 (Apse, 1996~. Even a small 10,000 Btu-per-hour unvented gas heater, about one-tenth the ca- pacity of a residential furnace system, would release water vapor equivalent to about 10 L per day of liquid water (Apse, 1996~.

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INDOOR DAMPNESS AND ASTHMA 301 faces of walls of air-conditioned buildings has been associated with moisture problems behind the wallpaper (Lstiburek and Carmody, 1994; Rose, 1994~. In mechanically ventilated buildings, pressure differences be- tween indoors and outdoors or between indoors and the sur- rounding soil are generated by mechanically produced airflows. These pressure differences modify the rates of moist air transport through the building envelope in a manner that may inhibit or increase indoor moisture problems. In cold climates, the design intent is often to maintain buildings Repressurized relative to out- doors and to prevent humid indoor air from flowing outward through the building envelope. In warm, humid climates, pres- surization of the building to limit infiltration of humid outdoor air is usually the design intent. Because houses rarely have con- tinuously operating mechanical ventilation systems, outdoor air infiltrates into the building through portions of the building en- velope and indoor air exfiltrates through other sections of the en- velope. Based on this discussion, the risk factors for moisture prob- lems include water leaks from the building interior or exterior; unusually high rates of water vapor generation indoors; a high rate of moisture entry into buildings from moist soil (often associ- ated with problems in water drainage around foundations); a low rate of ventilation particularly during the winter (see Chapter 10~; the absence or improper location of vapor barriers; insufficient water vapor removal by dehumidifiers or air-conditioning sys- tems; and an unusually cold or unusually humid climate. The prevalence of these different risk factors and the implications for microbiological growth are not well documented; however, water leaks are very common (see below) and cited in many case stud- ies of building-related respiratory health problems. Measures of Dampness Moisture Measurements Temperature and relative humidity measurements are the fundamental information regarding moisture in buildings. Hu- midity is usually measured psychometrically and is represented

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302 CLEARING THE AIR as relative humidity the amount of water in the air relative to the amount of water the air can hold at saturation at the same temperature and pressure. At present there are no accepted protocols for characterizing the moisture levels of buildings. However, wide variations in both temperature and humidity are to be expected from place to place and over time, daily and seasonally. Given this variation, moni- toring may be necessary to track environmental changes over time. The design of a monitoring system depends on the type of information one desires. Building monitoring may be designed to disclose center-of-room moisture conditions, moisture conditions at particular (perhaps troublesome) locations, response of the building to exterior conditions such as the entry of rainwater, moisture movement within the building, and change in humidity conditions over time. However, monitoring cannot be used to dis- cern the appearance of undesirable conditions away from where instruments are placed, nor can it be used to determine that all moisture-related aspects in a building are acceptable. There are a wide variety of tools available for measuring spe- cific moisture conditions (Lagus, 1994~. Infrared pyrometers can be used to identify surface temperature anomalies, which may become moisture and mold sites. Pin-type moisture meters mea- sure material moisture content, although calibration difficulties may limit their effectiveness. Smoke pencils can help identify en- velope leakage sites and also the effectiveness of combustion product discharge. Pressure difference instruments (manometers and micromanometers) may be employed to estimate the role of air pressure and movement in the development of water prob- lems in building envelopes. Abe and colleagues (1996) developed a sensor for determin- ing the ability of fungi to grow in microenvironments. The method uses an agar medium impregnated with spores of a xerophilic fungus and relies on water absorption from the envi- ronment to stimulate fungal growth. Microclimate differences and changes were documented in an apartment using the method. Visible Signs of Dampness Although humans are poor humidity sensors, there are signs

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INDOOR DAMPNESS AND ASTHMA 303 of inappropriate moisture conditions that can be directly per- ceived. Such perceptions are the basis for most epidemiologic studies in which moisture condition data are collected by ques- tionnaire. Questions are typically formulated to seek information on whether conditions such as leaks, floods, wet basements, win- dow condensation, visible fungal growth, or moldy odors are cur- rently present or have been present in the past. It should be noted, however, that reporting bias is an important source of error in such studies. Dales and colleagues (1997) report that under some conditions, allergy patients may be more likely than nonallergic people to report visible fungal growth. Additionally, smokers may be less likely than nonsmokers to report such growth. Moisture conditions in buildings are best discovered through direct observation and inspection. Home inspectors are known to rely on smell to supplement visual inspection. Among the items typically included in an inspection report are presence of mold, water stains, evidence of leaks or flooding, current leaks, craw! space conditions, attic sheathing condition, and overall stoutness or dilapidation of the building. Characterization of rainwater dis- charge and management is also necessary, given the importance and prevalence of foundation leakage to the overall moisture bal- ance of a building. Extent of the Home Dampness Problem The reported percentage of homes with dampness problems varies widely depending on geography, the approach to home selection, and the types of questions or inspection procedures used to detect such problems. Selected study results are presented in Table 8-1. The U.S. Census collects data on water leakage in homes. The results for 1973-1984 are reported in the Annual Housing Survey. Results after 1984 are reported in the American Housing Survey for the United States. Based on these data, Figure 8-1 shows the percentage of homes with water leakage from indoor and out- door water sources. The overlap between these categories and the total percentage of homes with water leakage are not reported. The reported percentages of homes with water leaks are relatively constant, and most water leaks are from outdoors. Based on the

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INDOOR DAMPNESS AND ASTHMA 21 - . 19 17 15 1 3 ~ 1 1 1 1985 1 987 ~ l 1989 1 991 305 Water Leakage from Inside of Structure < Water Leakage from Outside of Structure -~3 l 1993 1 995 FIGURE 8-1 Prevalence of water leaks in U.S. housing, based on data from the U.S. Census. data in Table 8-1 and Figure 8-1, a substantial portion of homes have moisture problems. Underlying Causes of Moisture Problems Although extensive guidance is available on means of pre- venting and remediating moisture problems in both residential and commercial buildings (e.g., Trechsel, 1994, chapters 15-22), moisture problems are very common. Economic and institutional barriers contribute to moisture problems. For example, water leaks will not be repaired if financial resources are inadequate. Also, the relevant features of building design, operation, and maintenance may be determined substantially by speculative builders or other decision-makers who are substantially unaf- fected by future moisture problems. Similarly, landlords who do not reside in the affected building may not be motivated to repair water leaks rapidly. Despite the technical knowledge about prevention of mois- ture problems that is available in current scientific and engineer- ing literature, the errors in building design and construction re- ported in case studies indicate that many architects, engineers, builders, and roofers have an inadequate knowledge of the means of preventing moisture problems. Additionally, these profession- als and tradesmen, and the general public, may not fully under- stand the association between moisture problems and health problems. The lack of awareness of health consequences reduces the motivation to prevent or correct problems.

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306 CLEARING THE AIR Moisture and Sources for Disease Agents The relationship between dampness and respiratory disease is considered to be linked to allergens or other materials derived from fungal growth, or dust mites, or both, although none of these pathways has been clearly documented. Billings and Howard (1998) reviewed the literature on indoor dampness and respira- tory disease and concluded that dampness increases allergen bur- den, leading to increased risk of developing asthma. Fungi Fungi are among the more versatile organisms with respect to water requirements and are able to grow with extremely little moisture under some conditions. Fortunately, conditions in build- ings do not usually permit such growth, which occurs only under optimal substrate and temperature conditions for the fungus. The majority of fungal growth occurs on surfaces that are continu- ously wet for many days. Such wetness may occur on cold sur- faces where condensation is continuously present, in materials that remain at or near the dew point (e.g., carpeting on uninsulated cold or damp surfaces), or in materials that get wet as a result of leaks or floods. Fungal growth can also occur with- out the presence of liquid water from leaks or condensation. High relative humidities (e.g., greater than approximately 80%) in- crease the risk of fungal growth on some surfaces (Foarde et al., 1996~. It should be noted that indoor middle-of-the-room humid- ity is not a consistent predictor of the presence of fungal growth, and fungal control cannot be achieved just with ambient indoor air humidity control. Fungi grow on surfaces under microenvi- ronmental conditions that may be very different from those in room air (Li and Hsu, 1997~. Data are equivocal on the relationship of airborne fungi to humidity or other dampness indicators. Verhoeff and colleagues (1992) found only a weak relationship between airborne fungi and dampness as characterized by a checklist. On the other hand, Garrett and colleagues (1998) found associations between high airborne fungal concentrations and musty odor, water intrusion, limited ventilation, and high indoor humidity. Relatively weak

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INDOOR DAMPNESS AND ASTHMA 307 relationships have also been shown for dampness indicators and concentrations of some fungi in dust (Dales et al., 1997; Douwes et al., 1999~. Visible fungal growth has been associated with high airborne concentrations of some fungi but not others. However, good studies examining the association between surface and air- borne fungi are lacking. Dust Mites Dust mite populations have been shown experimentally to respond to increasing humidity (Arlian et al., 1998~. Dust mite allergen concentrations have been associated with humidity and signs of dampness (Couper et al., 1998; Julge et al., 1998; Nicolai et al., 1998; van Strien et al., 1994), as well as with conditions known to lead to dampness such as increasing number of occu- pants and reduced ventilation (Couper et al., 1998; Sundell et al., 1995; van Strien et al., 1994~. Chapter 5 contains a discussion of the influence of humidity levels on dust mites. INDOOR DAMPNESS AND RESPIRATORY DISEASE Overview Table 8-2 summarizes studies that report odds ratios (ORB) for the association of dampness or visible mold with asthma. Ronmark and colleagues (1998) ranked home dampness sec- ond only to family history as a risk factor for asthma in northern Sweden. Die and colleagues (1999) report an association between ventilation rate and dampness in the home and bronchial obstruc- tion during the first year of life. The OR for bronchial obstruction related to dampness in low-ventilation homes was 9.6 (confidence interval [CI] 1.05-87.4~; in high ventilation homes the OR was 2.3 (CI 0.83-6.39~. Connections between animal allergens, dampness, and asthma have been made in several studies. Norback and col- leagues (1995) report that symptoms related to asthma were more common in dwellings with house dust mites and visible signs of dampness or microbial growth. However, a later study by some of the same individuals (Norback et al., 1999) reports no connec

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308 TABLE S-2 Oclcls Ratios (ORB) for Association of Dampness or Visible Molcl with Asthma CLEARING THE AIR Author/ Population Dampness OR (Cl) for Asthma Location (N) Indicator Related Health Effect Aldous et al., Infants (936) Presence or absence of 1.8 (1.1-3.0Ja 1996 (Arizona) evaporative cooler Nafstad et al., Children: Questionnaires, 3.8 (2.0-7.2Ja 1998(Norway) 251 cases, homevisits 251 controls Yazicioglu et al., Children: Questionnaire 2.62 (1.13-6.81Jb 1998 (Turkey) 597 controls, 85 asthmatics Yang et al., 1 998b Children: Reported dampness 1.77 (1 .24-2.53Jb (Taiwan) 86 cases, 86 controls Norback et al., Adults: Observed dampness Overall: 1.8 (1.1-3.0Jb 1999 (Sweden) 98 asthmatics, Floor: 4.6 (2.0-10.5Ja 357 controls Jaakkola et al., Children (2,568) Any dampness or mold 1.10 (0.54-2.24)b 1993 (Finland) 2.17-2.62a Slezak et al., Head Start Signs of dampness, 4.5 (1.25-16.3Jb 1998 (U.S.) children visible mold 1.94 (1.23-3.04Jb (1 ,085) Hu et al., 1997 Young adults Mold growth 2.0 (1.2-3.2Jb (2,041 ~ Brunekreef et al., Children Dampness and mold 1.27-2.12a 1989 (Netherlands) (4,625) Strachan, 1988 Children Visible mold 3.0 (1.72-5.25Ja (Scotland) (873) Yang et al., 1998a Children: Reported dampness 2.65b (Taiwan) 165 cases, 165 controls Nicolai et al., 1998 Adolescents Observed dampness 16.14 (3.53_73.73Ja (Germany) (1 55) Jedrychowski and Children Reported dampness 1.6 (1.1-2.5Ja Flak, 1998 (Poland) (1,129) NOTE: Cl = confidence interval. aWheeze, persistent cough, bronchial obstruction. bAsthma.

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INDOOR DAMPNESS AND ASTHMA 309 lion between allergy to dust mites and either current asthma or home dampness in Sweden. In another study, positive skin tests to dust mite allergens were more prevalent among occupants of damp houses than among occupants of homes without reported signs of dampness (Iversen and DahI, 1995~. Lindfors and col- leagues (1995) report that a combination of high-dose exposure to cat or dog allergen, environmental tobacco smoke, and damp housing was significantly associated with asthma (OR = 8.0; CI 1.9-34.1~. Williamson and colleagues (1997) report a correlation between mold growth indicators and asthma (196 age- and sex-matched subjects): r = 0.23, p < .035. Norback and colleagues (1999) report that allergy to fungi (CIadosporium or Alternaria) was more preva- lent in damp homes (9.3% versus 3.9%) and fungal sensitivity was related to current asthma (OR = 3.4; CI 1.4-8.5~. Brunekreef and colleagues (1989) studied 4,625 children relating symptoms and pulmonary function to reported dampness and molds in the homes. The OR for reported molds varied from 1.27 to 2.12. There was a drop in FEF25_75 of 1.6% associated with reported mold. Among a population sample of 873 children, Strachan (1988) stud- ied respiratory symptoms, measured pulmonary function, and evaluated the home environment for reported dampness or mold. Wheezing in the past year was most closely associated with vis- ible mold (adjusted OR = 3.0; CI 1.72-5.25~. However, there was no association with the degree of bronchospasm in children mea- sured in homes with and without mold; the association may be due to awareness of mold leading to increased reporting. The prevalence of lower-respiratory symptoms (any cough, phlegm, wheezing, or wheeze with dyspnea) was increased among those reporting dampness or mold compared with those not reporting dampness or mold as follows: 38% versus 27% among current smokers, 21% versus 14% among ax-smokers, and 19% versus 11% among nonsmokers (all p values < .001~. Mater and col- leagues (1997) indicate an association between reported house- hold water damage and physician-diagnosed asthma in Seattle school children.

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310 CLEARING THE AIR Conclusions Regarding Health Effects 1. Damp conditions are associated with the existence of doc- tor-diagnosed asthma and with the presence of symptoms con- sidered to reflect asthma (i.e., dampness may lead to the develop- ment of asthma). 2. Symptom prevalence among asthmatics is also related to home dampness indicators (i.e., dampness may exacerbate exist- ing asthma). 3. The factors related to dampness that actually lead to the development of disease and to disease exacerbation are not yet confirmed, but probably relate to dust mite and fungal allergens. DAMPNESS CONTROL Implementation of measures that are effective in reducing dampness problems should be a logical approach to lessening the indoor asthma problem. Several recommendations for prevention and remediation of moisture problems, including periodic inspec- tions to prevent water leakage, are provided in a review article based on a workshop held by the American Thoracic Society (ATS, 1997~. However, no intervention studies clearly document that any form of dampness control works effectively to reduce symp- toms or to reduce the chances of asthma development. Rose (1994) provides recommendations for retrofitting existing buildings for dampness control. Peat and colleagues (1998) suggest that retrofit- ting for dampness control is expensive and unlikely to have long- term beneficial effects, and that houses be designed to prevent dampness problems. Logical steps can be taken to reduce dampness problems, and most have been documented as effective. For houses, these steps include 1. powered mechanical ventilation to remove and/or dilute occupant-generated moisture (Harrje, 1994~; 2. proper installation of vapor barriers (Lsteburek and Carmody, 1993~; 3. channeling ground water away from foundations and seal

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INDOOR DAMPNESS AND ASTHMA 311 ing below-ground walls to prevent water intrusion (Lstiburek and Carmody, 1994~; 4. properly protecting ground-level concrete slabs from mois- ture intrusion (Lstiburek and Carmody, 1994~; and 5. constructing craw! spaces to prevent water intrusion (Lstiburek and Carmody, 1994~. RES"RCH NEEDS With respect to the association of dampness problems with asthma development and symptoms, research is needed to clearly identify the causative agents (e.g., molds, dust mite allergens) and to document more accurately the relationship between dampness and allergen exposure. Research is also needed to characterize and demonstrate the reductions in asthma morbidity from pre- vention or remediation of moisture problems. Regarding characterization of moisture problems, research is needed to: 1. develop accurate, standardized protocols for assessing moisture problems in buildings; 2. develop and document the effectiveness of specific mea- sures for dampness reduction in existing buildings; and 3. develop standardized, effective protocols for flood cleanup that will limit microbial growth. In addition to these research needs, there is a need for improved education of the public about the consequences of moisture prob- lems and for better education of building professionals regarding means of preventing moisture-related problems. REFERENCES Abe K, Nagao Y. Nakada T. Sakuma S. 1996. Assessment of indoor climate in an apartment by use of a fungal index. Applied and Environmental Microbiology 62(3):959-963.

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312 CLEARING THE AIR Aldous MB, Holberg CJ, Wright AL, Martinez FD, Taussig LM.1996. Evaporative cooling and other home factors and lower respiratory tract illness during the first year of life. American Journal of Epidemiology 143~5~:423-430. ATS (American Thoracic Society).1997. Achieving Healthy Indoor Air. Report of the ATS Workshop: Santa Fe, New Mexico, November 16-19, 1995. American Journal of Respiratory and Critical Care Medicine 156~3~:S33-S64. Apte MG. 1996. Unvented gas space heaters: drainless sinks. Home Energy 13~5~:9-10. Arlian LG, Confer PD, Rapp CM, Vyszenski-Moher DL, Chang JC. 1998. Population dynamics of the house dust mites Dermatophagoides farinae, D. pteronyssinus, and Euroglyphus maynei (Acari: Pyroglyphidae) at specific relative humidities. Journal of Medical Entomology 35~1~:46-53. Billings CG, Howard P. 1998. Damp housing and asthma [Review]. Monaldi Archives for Chest Disease 53~1~:43-49. Brunekreef B. 1992. Damp housing and adult respiratory symptoms. Allergy 47~5~:498-502. Brunekreef B. Dockery DW, Speizer FE, Ware JH, Spengler JD, Ferris BG. 1989. Home dampness and respiratory morbidity in children. American Review of Respiratory Disease 140~5~:1363-1367. Christian JE. 1994. Moisture Sources. In Moisture Control in Buildings, Trechsel HR, Ed. American Society for Testing and Materials, Philadelphia. Couper D, Ponsonby AL, Dwyer T. 1998. Determinants of dust mite allergen concentrations in infant bedrooms in Tasmania. Clinical and Experimental Allergy 28~6~:715-723. Dales RE, Burnett R. Zwanenburg H. 1991. Adverse health effects among adults exposed to home dampness and molds. American Review of Respiratory Disease 143~3~:505-509. Dales RE, Miller D, McMullen E.1997. Indoor air quality and health: validity and determinants of reported home dampness and moulds. International Journal of Epidemiology 26~1~:120-125. Douwes J. van der Sluis B. Doekes G. van Leusden F. Wijnands L, van Strien R. Verhoeff A, Brunekreef B. 1999. Fungal extracellular polysaccharides in house dust as a marker for exposure to fungi: relations with culturable fungi, reported home dampness, and respiratory symptoms. Journal of Allergy and Clinical Immunology 103~3 Pt 1~:494-500. Flannigan B. Morey PR. 1996. Control of moisture problems affecting biological indoor air quality. ISIAQ guideline TFI-1996. Ottawa, Canada: International Society of Indoor Air Quality and Climate. Foarde KK, Van Osdell DW, Chang JCS. 1996. Evaluation of fungal growth on fiberglass duct materials for various moisture, soil, use and temperature conditions. Indoor Air 6~2~:83-92. Garrett MH, Rayment PR, Hooper MA, Abramson MJ, Hooper BM.1998. Indoor airborne fungal spores, house dampness and associations with environmental factors and respiratory health in children. Clinical and Experimental Allergy 28~4~:459-467.

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