Fungal Contamination in Public Buildings: Health Effects and Investigation Methods

2. Health Effects of Indoor Molds (Continued)

2.1.2 Case-control studies

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.

• In the Netherlands, a nested case-control study was carried out within a random sample of 7,632 children aged 6 to 12 years whose parents had completed a screening questionnaire. Cases were selected among children with reported asthma (n=76), chronic cough (n=81) or other respiratory conditions, for a total of 259. Controls (n=257) were selected among children without respiratory symptoms. Data were collected through a self-administered questionnaire to parents and through a visit to all participants' homes by a trained investigator blind to children's case or control status. Crude odds ratios were calculated: reported mold somewhere in the houses was associated with an increased risk of chronic cough (OR 1.90, 95% CI 1.02 to 3.52), reported mold in the living room with physician-diagnosed asthma (OR 2.95, 95% CI 1.34 to 6.52) and reported mold in the bedroom with chronic cough (OR 3.52, 95% CI 1.55 to 8.03). No significant association was found with the presence of mold observed by the investigator. Adjusted odds ratios were also calculated, and were mostly lower than the corresponding crude odds ratios. When cases with elevated Imunoglobulin E (IgE) antibodies to molds and/or dust mites were compared to controls without IgE to these allergens, mold exposure observed by the investigator was found to be associated with sensitization + physician-diagnosed asthma (crude OR 2.61, 95% CI 1.21 to 5.64) and sensitization + chronic cough (crude OR 3.45, 95% CI 1.20 to 9.93) (Verhoeff et al. 1995).
  
  
• In the United Kingdom, 486 cases who had frequent or speech-limiting wheezing in the previous 12 months, and 475 controls, selected from participants in a previous health survey, were included in a case-control study. Participants were aged 11 to 16 years. Exposure classification was based on damp or mold in the chil dren's bedroom: "none," "damp only" and "damp with mold." In univariate analysis, no association was found between damp bedroom (without mold) and asthma (unadjusted OR 0.85, 95% CI 0.39 to 1.83), but the presence of both dampness and mold in the bedroom was associated with an increased risk of wheezing (crude OR 2.20, 95% CI 1.11 to 4.43). For the multivariate analysis, the mold/dampness variable was dichotomized into "none" and "any mold," and was no longer associated with wheezing (Strachan and Carey 1995).
  
  
• In the United Kingdom, 102 patients with physician- diagnosed asthma, aged 5 to 44 years and 196 population controls were interviewed by a trained interviewer about their respiratory health and their housing conditions. After the interview, subjects were asked to have their house inspected by a surveyor blind of their case or control status, and 222 out of 298 participants agreed. Odds ratios were adjusted for age, gender, income, unemployment, smoking, other smokers living in homes, and pets. When self-reported exposure was considered (283 participants included), asthma was associated with the presence of "any dampness" (OR 1.93, 95% CI 1.14 to 3.28) or "severe dampness" (OR 5.45, 95% CI 2.81 to 10.6), with dampness in previous home (OR 2.55, 95% CI 1.49 to 4.37), and with having moved because of dampness in previous home (OR 2.08, 95% CI 1.02 to 4.24). When exposure observed by the surveyor was considered, asthma was associated with the presence of "any dampness" (OR 3.03, 95% CI 1.65 to 5.57) and "severe dampness" (OR 2.36, 95% CI 1.34 to 4.01), but not with the presence of mold (OR for "severe mold": 1.70, 95% CI 0.78 to 3.71) (Williamson et al. 1997).

Table 4. Case-control studies on asthma and exposure to indoor molds, 1995 to 2001

Click to enlarge table

• In Sweden, a nested case-control study was carried out among individuals aged 20 to 44 who participated in a respiratory health survey, and who agreed to undergo a lung function examination and a bronchial challenge test with methacholine, and to provide a blood sample. Ninety-eight cases had current asthma, defined as a combination of bronchial hyperresponsiveness and either wheezing or breathlessness in the past 12 months, and 357 controls had no current asthma. Exposure assessment was based on questionnaire data. Odds ratios were adjusted for age, gender and smoking. Current asthma was associated with water damage or flooding in dwellings (OR 1.8, 95% CI 1.002 to 3.2) and dampness signs on the floor (OR 4.6, 95% CI 2.0 to 10.5), and a similar but non-significant trend was found for visible mold on indoor surfaces (OR 1.9, 95% CI 0.93 to 3.8). A stratified random sample of 88 dwellings was inspected by an occupational hygienist who recorded signs of building dampness as requested in the questionnaire. There was a good agreement between participants' and the occupational hygienist's report on water damage (Cohen's Kappa 0.40, ρ=0.001) and visible mold (Cohen's Kappa 0.36, ρ=0.004) (Norbäck et al. 1999).
  
  
• In Austria, a subset of 1,781 participants in a health survey of children aged 6 to 9 years was used for a case-control study. Cases were those who answered "yes" to the question "wheezing in the past 12 months?" and controls were those who answered "no" to that question. Odds ratios were adjusted for age, gender, parents' or sibling's history of asthma, parental education and exposure to environmental tobacco smoke. Dampness or mold at home was significantly associated with wheezing (OR 1.43, 95% CI 1.24 to 1.65) (Zacharasiewicz et al. 1999).
  
  
• In Sweden, a nested case-control study was carried out among respondents aged 20 to 50 years to a questionnaire-based survey. Cases were those who reported asthma diagnosed by a physician at age 16 or older, and controls were randomly selected among the survey participants. Selected participants were sent a comprehensive questionnaire regarding their health, their home environment and other risk factors. Odds ratios were computed using a logistic regression controlling for gender, sex, smoking habits and atopy. Visible mold growth in any of the six latest homes inhabited was significantly associated with asthma (OR 2.2, 95% CI 1.4 to 3.5), and this association remained significant after controlling for visible dampness (OR 2.4, 95% CI 1.3 to 4.2) (Thorn et al. 2001).
  
  
• In Canada, a nested case-control study was carried out among children aged 5 to 19 in two communities in Alberta. Participants were selected from among those whose parents had responded to a mail-out questionnaire. Five hundred and ninety-two cases were randomly selected among those with a current physician-diagnosed asthma, and 443 controls were selected among those with no history of asthma. Data on demographic, environment, medical history and host factors were collected by telephone interviews. Odds ratios and confidence intervals were calculated using unconditional logistic regression, including potential confounders: gender, age, gas cooking, parental asthma and allergies, and number of siblings. Exposure to indoor molds or mildew in the past year was significantly associated with asthma (OR 1.6, 95% CI 1.1 to 2.3) (Hessel et al. 2001).
  
  
• In Finland, a case-control study was carried out in adults aged 21 to 63 years. Cases were newly diagnosed asthma cases and controls had no previous or current asthma. Odds ratios were adjusted for gender, age, parental atopy or asthma, education, smoking, environmental tobacco smoke exposure, pets and occupational exposures. No association was found between dampness or mold exposure in the home and asthma. Conversely, visible mold or mold odour at work was associated with a higher risk of adult-onset asthma (OR 1.54, 95% CI 1.01 to 2.32). No such association was found between dampness or water damage, and asthma (Jaakkola et al. 2002).