European Journal of Epidemiology 13: 547–552, 1997. 1997 Kluwer Academic Publishers. Printed in the Netherlands.
The association of respiratory problems in a community sample with self-reported chemical intolerance C.M. Baldwin1,2,3, I.R. Bell3,4,6, M.K. O’Rourke1,2,5 & M.D. Lebowitz1,2,5 1
The Respiratory Sciences Center, Departments of 2 Medicine, 3 Psychology, 4 Psychiatry, Family and Community Medicine, 5 Arizona Prevention Center, University of Arizona, USA; 6 Department of Psychiatry, Tucson Veterans Affairs Medical Center, Tucson, Arizona, USA Accepted in revised form 3 December 1996
Abstract. This epidemiological study evaluated respiratory histories in those individuals reporting chemical intolerance (CI) in a community population sample. The subsample of 181 completed standard Respiratory Health Questionnaires. CI was determined from self-ratings of feeling ‘moderately’ to ‘severly’ ill from exposure to at least three of five common chemicals (paint, pesticides, car exhaust, new carpet, and perfume); the prevalence rate was 22.7%. The comparison group (CN) (31.5% of the sample) were selected from their reports of ‘never’ feeling ill from the same chemicals. The prevalence rate of CI in females was over twice that in males (28% vs 12.9%), a significant difference. There were
no significant differences in smoking, age, or education between CI and CN. Prevalence rates for symptoms and Relative Risk Ratios (RR) indicated that the CI were significantly more likely to report chronic cough, phlegm, wheeze, chest tightness, exertional dyspnea, acute respiratory illnesses, hay fever, child respiratory trouble, and physician confirmed asthma. Several of these respiratory symptoms were significantly, though differentially, related to ‘current’ asthma and hay fever reports. Results suggest a potential vulnerability to and greater interference from respiratory illness for the CI, which have implications for women's health and quality of life.
Key words: Chemical intolerance, Epidemiology, Quality of life, Relative risk ratio, Respiratory health, Women’s health Abbreviation: CI = chemical intolerance; CN = chemically neutral
Introduction Illness associated with the odors of common chemicals such as cleaning agents, perfume, car exhaust, and pesticides is emerging as a potentially important public and environmental health concern [1, 14]. Reported estimates of prevalence rates of marked chemical intolerance (CI) range up to 30% in clerical workers at an EPA building [28]. A form of CI found in solvent-exposed occupational groups may have prevalence rates which reach 60% [19]. Bell and colleagues have published prevalence rates of reported CI in college students, middle-aged women, and community-living elderly samples of 10–30% [3–7]. CI is associated with a clinical picture that can include symptoms of fatigue, anxiety, depression, attention and concentration problems, irritability, tachycardia and/or palpitations [3–7, 19]. In addition, ancillary evidence suggests that odors worsen asthma [24]. Symptoms of extreme CI (sometimes called multiple chemical sensitivity) may be chronic, severe, disabling, and costly to the individual and society [8].
Despite the growing attention being accorded the complex symptomatology of CI, little systematic research has been done to examine the prevalence rates of presenting symptoms, or natural history of the disorder [20]. A logical step would be to investigate respiratory complaints, since those individuals with CI state they become ill from inhalation and the ‘odor’ of common chemicals. Epidemiology has played a crucial role in elucidating complex symptomatologies, such as in CI [20]. Thus, the aim of this study is to describe the prevalence rates of reported respiratory symptoms, asthma and hay fever, their relation to CI, and to demographic characteristics in a representative subset of a population study.
Materials and methods Population. Subjects for this research were derived from a stratified cluster population study of Pima County municipal employees and their families recruited in 1985–1986, who lived in Tucson,
548 Arizona, USA, as described previously [21]. This population was representative of the urban area employed population, including a representative distribution of age, sex and ethnicity [21]. The intent of the study was to investigate relationships between indoor and outdoor air contaminants on respiratory health. Participants and survey/questionnaire materials. During a follow-up study in 1992–1993, the last 200 individuals were asked to respond to questions from the Chemical Odor Intolerance Index (CII) [27]; 181 (90%) did so. These participants were informed that this study was a continuation of the original health and environment research. Participants were not aware of the intent of the CII, nor were they told that this measure was used to assess chemical intolerance. These steps were taken to reduce the chance of information and/or selection bias. The CII is a 5-point Likert scale screening index of five everyday chemicals (paint, pesticides, new carpet, car exhaust, perfume), summed on self-rated frequency of illness. These five substances have been demonstrated as illness-provoking odors by other researchers [10]. The Chemically Intolerant (CI) were determined from their self-ratings of feeling ‘moderately’ to ‘severely’ ill from exposure to at least three of five common chemicals. The Chemically Neutral (CN) were selected based on their self-reports of ‘never’ becoming ill from the same five chemicals. Scores for the CI in this study ranged from 15 to 25, while scores for the CN did not tally above five, as described previously [3–7]. The CII has shown strong reliability and factorial validity on studies of nearly 2,000 individuals; Cronbach's alpha was 0.80 for college student samples, 0.92 for community-living elderly men and women, and 0.90 for CI and multiple chemically sensitive (MCS) women involved in a quasi-experimental laboratory study [5]. Normative and group validity data indicated the CI were prone to score higher on the CII than the general population [27]. Correlations between the CII and several biobehavioral constructs related to chemical odor intolerance, such as noise sensitivity and limbic system dysfunction [3, 5], have also shown highly significant consistent and positive relationships [27]. In addition to the CII, participants completed a standard Specialized Center of Research (SCOR) Respiratory Health Questionnaire [15, 25]. These questions were validated by comparisons to lung function [13]; this paper also showed good correspondence between self-completion and intervieweradministered questionnaires. Along with questions regarding their respiratory health and symptomatology in this study, participants were queried as to their ‘current’ asthma and hay fever status. If ‘Yes’, questions regarding physician confirmed asthma or
hay fever ensued. The questionnaire completed by this subset of individuals has demonstrated correspondence of symptoms with physician diagnosed clinical evaluations [16]. Methods of analysis. Chi-square [26] was used to compare the CI and CN on their respiratory health histories, as well as stratified analyses of respiratory symptoms by ‘current’ reports of asthma. Relative risk ratios (RR) were calculated as the ratios of the prevalence rates of CI and CN for each of the respiratory complaints. In most cases, Fisher’s Exact Test was used to provide the p value for RR results [29]. The likelihood ratio (LR) was used in some comparisons, as indicated accordingly in the results section.
Results Prevalence rates of CI and CN were 22.7% and 31.5%, respectively. There were significantly more women in the CI group (78%) compared to the CN group (50.9%), and in the total sample (61.3%) (Table 1). There were no significant differences for age between groups. The CI group had fewer ethnic minorities (5% vs 10%). Mean number of years of education was 14 in both groups, and marital status was similar. CI was not related to smoking. Prevalence rates for respiratory symptomatology/history Prevalence rates of self-reported respiratory symptomatology for the CI and CN are shown in Table 2. Significantly higher prevalence rates (> 3-fold) were found in the CI compared to the CN. These higher rates of symptoms involved the various respiratory conditions, namely productive cough (bronchitis), exertional dyspnea, wheezing and asthma complaints, and hay fever. Responses to more serious conditional questions about wheezing and attacks of wheezing dyspnea showed many more CI than CN to report wheeze apart from colds (a significant trend) and attacks of wheezing dyspnea apart from exertion. The CI were nearly twenty times more likely to report chest tightness apart from exertion compared to their CN cohorts on a conditional question; however, this finding was not significant due to small numbers. The relative risk for Grade 3+ exertional dyspnea (a more serious complaint), based on the survey question ‘Do you get short of breath walking with people of your own age on level ground?’, was seven times greater for the CI compared to the CN (statistically significant). Further, 35.7% of CI compared to 4.3% of CN were told by a physician that this was due to asthma, bronchial trouble, or emphysema; 7% of CI, but no CN, were told by a physician that the Grade 3+
549 Table 1. Characteristics of the studied population CI % (N)
CN % (N)
Neither % (N)
Total %
Sex (n = 181) Male Female
22 0(9) 78 (32)*
49 (28) 51 (29)
40 (33) 60 (50)
039 061
Age (n = 176a) 15–39 40–49 50+
20 0(8) 38 (15) 42 (17)
15 0(8) 40 (22) 45 (25)
36 (29) 38 (31) 25 (21)
025.6 038.6 035.8
Ethnicity (n = 161b) Non-Hispanic white Other
95 (35) 05 0(2)
90 (46) 10 0(4)
89 (65) 11 0(9)
091 009
a
5 with missing age. 20 with missing ethnicity. * p < 0.05 (vs CN and total).
b
Table 2. Prevalence rates of respiratory complaints reported by chemically intolerant (CI) and neutral (CN) individuals CI % (N)
CT % (N)
RR
Cough Morning only At any time
30 (27) 40 (27)
14 (50) 12 (50)
02.11 (n.s.) 03.39 ( p < 0.01)
Mucous production Morning only At any time
37 (27) 25 (27)
06 (49) 06 (49)
06.07 ( p < 0.001) 04.24 ( p < 0.05)
Wheezing Without a cold
50 (28) 39 (28)
17 (47) 02 (47)
02.94 ( p < 0.01) 18.70 ( p = 0.07)*
Attacks of shortness of breath with wheeze + apart from exertion
37 (27) 37 (27)
13 (47) 06 (47)
02.89 ( p < 0.05) 05.78 ( p = 0.13)*
Chest tightness + apart from exertion
54 (28) 43 (28)
04 (46) 02 (46)
12.45 ( p < 0.00001) 19.50 ( p = 0.12)*
Exertional dyspnea grade 3+
30 (27)
04 (49)
07.22 ( p < 0.01)
Asthma Current physician confirmed
25 (28)
04 (48)
05.95 ( p < 0.05)
Current hay fever
78 (27)
47 (49)
01.66 ( p < 0.01)
Respiratory trouble < age 16
43 (20)
16 (57)
02.63 ( p < 0.01)
* Fisher exact (likelihood ratio p < 0.05).
exertional dyspnea was due to heart trouble. Neither of these findings achieved statistical significance, however. The risk for reported physician confirmed current asthma for the CI was nearly six times that of the CN ( p < 0.05). Of the CI with current hay fever, 45.5% indicated that they had seen a physician for this problem, compared to 15.2% of the CN. In addition, the CI were nearly three times as likely to self-report a history of respiratory trouble before age 16 years.
Stratified analysis of respiratory symptoms with ‘current’ asthma Stratified analysis of symptom rates by the presence of current asthma indicated that only 2 CN (and only 7 CI) had current asthma (as indicated in Table 2). However, the analyses comparing CI and CN prevalence rates in those without current asthma yielded very close to the same results as found for the total population (in Table 2). Some differences between CI and CN were actually larger after removing asthmatics, including cough, chest tight-
550 ness and exertional dyspnea. Thus, higher rates of symptoms found in CI were not necessarily due to their higher prevalence of asthma, and the effect of asthma on other symptom prevalence rates. The CI with asthma had higher prevalence rates of wheezing complaints and respiratory trouble before age 16 than CI without asthma. Inability to perform usual activities due to respiratory illness As shown in Table 3, when asked to indicate, during the year prior, how often they were unable to perform their usual activities due to illnesses such as chest colds, bronchitis, or pneumonia, the CI were 43% more likely to report ‘one such illness’ compared to the CN. However, the CI were nearly three and one half times more likely to report ‘two or more illnesses’ compared to the CN; the chi-square was significant ( p < 0.05). Table 3. Prevalence rates for respiratory illnesses reported to disrupt lifestyle during the previous year reported by chemically intolerant (CI) (n = 28) and neutral (CN) (n = 49) individuals Ill in past year
CI (%)
CN (%)
RR
One such illness Two or more illnesses
32 14
22 04
1.43 3.49 ( p < 0.05)
Discussion These present data replicate and extend previous studies. As in earlier research [3, 4, 6, 7], there are significantly more women among those reporting chemical intolerance. This investigation demonstrates increased prevalence rates of self-reported respiratory complaints in a community-based group of CI individuals. Respiratory symptomatology, stratified according to CI and CN reports of ‘current’ asthma, also showed increased prevalence rates in the CI. Further, the CI indicated an early history of respiratory trouble, suggesting a likely influence of a host susceptibility factor [9], or predisposition due to childhood respiratory problems. Other research supports these findings. Bascom [2] posited the respiratory mucosa as likely target and effector sites in CI. Meggs & Cleveland [18] reported increased nasal congestion in the CI, and suggested nasal pathology as a main feature of CI; Meggs [17] further suggested that inflammed airways is a sign of CI. Doty [11] found increased nasal resistance, as well as increased respirations and heart rates (suggesting more labored breathing) in persons with CI. The large female to male ratio (4:1) suggests that CI could be an overlooked sex-related problem
pertaining to health. Further studies on the nature of any sex-related host susceptibility factors in CI are warranted. These results may also be indicative of restricted activity in the CI, particularly for women, due to vulnerability to and interference from more respiratory illnesses. This, in turn, may imply a diminished quality of life, which needs to be explored further. The illness reports in this study, as well as likely increases in physician visits for current asthma and the other respiratory problems, may indicate greater health care utilization by the CI. This is consistent with other accounts. In a study of medical utilization that incorporated individuals who were self-reported to be sensitive to everyday chemicals, it was found that these individuals averaged 23.3 visits to a medical provider in the previous year [8]. We realize that there are potential drawbacks to this study. Most pronounced is the use of selfreported health histories in the absence of clinical measures and/or physician diagnosed clinical reports. However, epidemiologic-based research is highly dependent on the questionnaire-type format [16]. The standardized NHLBI and ATS questionnaires used in this study have been used extensively (with modifications) throughout the tenure of the Tucson 25 year study of airways obstructive disorder [15, 16, 25]; results have been shown to be both valid and reliable [15]. Further, although the survey instrument may show more variability, standard epidemiological questionnaires such as used here have been shown as suitable for surveys of chronic conditions, and responses have been consistent with clinical diagnoses in approximately 90% of individuals [16]. It is also important to note that self-reported asthma is strongly related to bronchial responsiveness, an objective indicator [22]. We selected nominal analyses using the chi-square statistic to provide prevalence rates and relative risk ratios due to the exploratory nature of this project, i.e., to describe any respiratory symptom related differences in a subset of a community-based survey sample, which included CI and CN individuals [12]. While there are a number of strong associations for the CI and their respiratory symptomatology that cannot be explained by chance alone, we are not suggesting that these results intend a cause/effect linkage. Rather, this descriptive study, via prevalence rates and relative risk, can serve as an heuristic for future research directions that can more appropriately address dose-response relationships. Findings in this study are intended to determine potential clinical/ epidemiological significance, as well as assist in developing future larger scale, epidemiologicallybased studies. Despite limitations, these findings appear relevant and stimulating. The results might suggest that an early history of childhood respiratory trouble (CRT) may predispose the CI to be ‘at risk’ for respiratory
551 problems. It would be worth studying further the hypothesis that CRT could possibly initiate greater sensitizability to chemicals and, likewise, greater vulnerability to illness from everyday chemicals.
11. 12.
Acknowledgments This study was presented in part at the 4th International Congress of Behavioral Medicine, Washington, DC, 13–16 March, 1996. This work was supported by NIH/NHLBI SCOR Grant HL14136. We wish to offer our appreciation to the participants, their families, and the research team members who made this study possible. We would also like to gratefully acknowledge the Kluwer Editorial Staff for their diligence, particularly Naomi Roest, and to the reviewers of this manuscript for their very thoughtful comments and suggestions. The authors extend their sincere thanks.
13.
14.
15.
16.
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Address for correspondence: Carol M. Baldwin, PhD, RN, University of Arizona, College of Medicine, Division of Respiratory Sciences (Rm 2348), 1501 North Campbell Avenue, Tucson, AZ 85724-5030, USA Phone: (520) 626-2047; Fax: (520) 626-6970 E-mail:
[email protected]
