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* From the Division of Environmental Hazards and Health Effects, National Center for Environmental Health; and Division of Adult and Community Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA.
Correspondence to: Earl Ford, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS E17, Atlanta, GA 30333; e-mail: esf2{at}cdc.gov
| Abstract |
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Design: Cross-sectional study of participants in 50 states in the United States.
Setting: Using data from 163,773 adult respondents in the 2000 Behavioral Risk Factor Surveillance System, we examined how self-reported asthma is associated with general self-reported health and four health-related quality-of-life measures.
Results: Participants with self-reported current asthma reported significantly more age-adjusted physically unhealthy days (6.5 days vs 2.9 days, p < 0.001), mentally unhealthy days (5.2 days vs 3.0 days, p < 0.001), days with activity limitation (3.7 days vs 1.6 days, p < 0.001), and unhealthy physical or mental days (10.0 days vs 5.4 days, p < 0.001) in the last 30 days than participants who never had asthma. After adjusting for age, sex, race or ethnicity, educational attainment, employment status, smoking status, physical activity status, and body mass index, the odds ratios among persons with asthma compared with persons who never had asthma, were 2.41 (95% confidence interval [CI], 2.21 to 2.63) for reporting poor or fair self-rated health, 2.26 (95% CI, 2.06 to 2.49) for reporting
14 days of impaired physical health during the previous 30 days, 1.55 (95% CI, 1.40 to 1.72) for reporting
14 days of poor mental health during the previous 30 days, 1.96 (95% CI, 1.73 to 2.21) for reporting
14 activity limitation days, and 1.99 (95% CI, 1.84 to 2.15) for reporting
14 days of physically or mentally unhealthy days during the previous 30 days. Results were consistent for all age groups, for both sexes, and for all race or ethnic groups. Participants who did not currently have asthma, but had it previously, reported having more unhealthy days with all four measures than participants who never had asthma, but fewer than participants who currently had asthma.
Conclusions: These results provide additional measures to evaluate and monitor the impact of asthma on the health of the US adult population.
Key Words: asthma quality of life survey
| Introduction |
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Although these numbers convey important information about the public health burden of asthma, other measures are needed to capture the full impact of a condition on the health of a population.5 6 Measuring health-related quality of life yields important information about the health of a population and how various conditions can have an impact on health. A number of standard assessment instrumentsusually known as generic questionnairesare available to measure overall health-related quality of life. The information generated from studies using these questionnaires may be helpful in guiding health policy decisions and influencing the allocation of health resources.7
To complement generic quality-of-life instruments and address issues specific to patients with asthma, researchers developed disease-specific quality-of-life questionnaires.6 Patient scores from these disease-specific questionnaires often correlate better with various physiologic measures and clinical indicators of asthma status than more generic instruments. Furthermore, changes in these scores are more sensitive to important but sometimes small changes experienced by patients with asthma. Traditionally, clinicians and researchers had used clinical or physiologic data to routinely evaluate the clinical status of patients with asthma. Such measures are clearly useful in clinical settings but do not address the full impact of asthma on the physical, psychological, emotional, and social well-being of these patients. Both generic and asthma-specific health-related quality-of-life measures are now routinely incorporated as outcomes in clinical trials of pharmacologic treatment and patient education strategies, and have been promoted for use in clinical practice by health-care providers as part of the management of their patients with asthma. Although the routine clinical use of quality of life instruments was not recommended by the National Asthma Education and Prevention Program, the expert panel did recognize the importance of following several dimensions of quality of life in patients with asthma.8
Researchers have shown that patients with asthma have impaired quality of life. However, significant gaps in our understanding of the effect of asthma on health-related quality of life remain.9 For example, few studies have examined the impact of asthma on quality of life at the population level.10 What little is known about the US population was based on studies that included only small samples or were not population based or representative of the population of the United States. Therefore, to better understand how asthma impacts the quality of life of the US population, we examined data from the 2000 BRFSS to examine the association between health-related quality of life and self-reported asthma in a large sample of US adults. We explored this relationship across age groups, among men and women, and among four racial or ethnic groups.
| Materials and Methods |
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18 years old in households with telephones. Respondents were asked, "Did a doctor ever tell you that you had asthma?" Those who responded "yes" were then asked, "Do you still have asthma?" Respondents who answered yes to both questions were classified as having "current" asthma. Respondents who answered yes to the first question but negatively to the second question were classified as having "former" asthma. Respondents who reported not having been told by a physician that they had asthma were classified as never having had asthma.
Four health-related quality-of-life questions were asked of participants in the BRFSS: (1) "Would you say that in general your health is: excellent, very good, good, fair, or poor?" (2) "Now thinking about your physical health, which includes physical illness and injury, for how many days during the past 30 days was your physical health not good?" (3) "Now thinking about your mental health, which includes stress, depression, and problems with emotions, for how many days during the past 30 days was your mental health not good?" and (4) "During the past 30 days, for about how many days did poor physical or mental health keep you from doing your usual activities, such as self-care, work, or recreation?" These BRFSS questions have good construct validity14 15 16 and reasonably good criterion validity with respect to the Medical Outcomes Study Short-Form 36 (SF-36) in both healthy and disabled populations.17 18
We used the following covariates: age, sex, race or ethnicity (non-Hispanic white, non-Hispanic African American, Hispanic, and other), educational attainment (never attended school or only attended kindergarten, grades 1 to 8, grades 9 to 11, high school graduate, some college or technical school, college graduate), employment status (employed for wages, self-employed, out of work for > 1 year, out of work for < 1 year, homemaker, student, retired, unable to work), smoking status (current, former, never), physical activity (inactive, irregular activity, regular activity, regular and vigorous activity), and body mass index. We directly adjusted the data for age to the 1980 US population. To examine whether self-reported asthma was independently associated with the quality-of-life measures, we developed logistic regression models with dichotomized quality of life measures as the dependent variable and self-reported asthma as the variable of interest adjusted for the covariates. When the sum of physically and mentally unhealthy days exceeded 30 days for an individual, we defined unhealthy days as 30 days. Thus, we assumed no overlap of unhealthy mental and physical days except for instances where it was obvious. We tested for effect modification by adding interaction terms for candidate effect modifiers and asthma status in multiple logistic regression models. We used the statistical software package Software for the Statistical Analysis of Correlated Data (SUDAAN; Research Triangle Institute; Research Triangle Park, NC), which was designed to analyze data from studies using complex sampling designs, to calculate proper SEs.19
| Results |
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14 days of impaired physical health (OR, 2.26; 95% CI, 2.06 to 2.49), to report having
14 days of impaired mental health (OR, 1.55; 95% CI, 1.40 to 1.72), to report having
14 days of activity limitations (OR, 1.96; 95% CI, 1.73 to 2.21), and to report having
14 days of impaired physical or mental health (OR, 1.99; 95% CI, 1.84 to 2.15) [Table 6 ].
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14 physically or mentally unhealthy days were 1.28 (95% CI, 1.07 to 1.52) and 1.74 (95% CI, 1.55 to 1.96) for participants with former and current asthma, respectively. For participants aged 45 to 64 years, the ORs were 1.42 (95% CI, 1.13 to 1.78) and 2.10 (95% CI, 1.84 to 2.38) for participants with former and current asthma, respectively. For participants aged
65 years, the ORs were 1.24 (95% CI, 0.85 to 1.80) and 2.55 (95% CI, 2.14 to 3.04) for participants with former and current asthma, respectively. For men, the ORs for reporting poor or fair health were 0.90 (95% CI, 0.68 to 1.18) for former asthma and 2.21 (95% CI, 1.92 to 2.54) for current asthma. For women, the ORs were 1.38 (95% CI, 1.11 to 1.73) for former asthma and 2.54 (95% CI, 2.28 to 2.84) for current asthma. For non-Hispanic whites, the ORs for reporting poor or fair health were 1.24 (95% CI, 1.04 to 1.47) for former asthma and 2.62 (95% CI, 2.37 to 2.89) for current asthma. For non-Hispanic African Americans, the ORs were 0.61 (95% CI, 0.34 to 1.08) for former asthma and 2.40 (95% CI, 1.86 to 3.10) for current asthma. For Hispanics, the ORs were 1.38 (95% CI, 0.86 to 2.22) for former asthma and 1.94 (95% CI, 1.49 to 2.51) for current asthma. For participants of another race or ethnicity, the ORs were 0.58 (95% CI, 0.29 to 1.17) for former asthma and 1.92 (95% CI, 1.24 to 2.97) for current asthma. | Discussion |
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Our results illustrate several important points. First, morbidity, as expressed by quality of life among adults with asthma, is substantial. They experience, on average, 10 days each month of impaired physical or mental health, almost double that of those who never have had asthma. Thus, the 14.7 million people with asthma in the United States experience approximately 147 million days of unhealthy physical or mental functioning, which is approximately 67.6 million excess days if they would have experienced the same number of days of unhealthy physical or mental functioning as people without asthma. Second, respondents with former asthma still report worse quality of life than those who never have had asthma. Whether this is due to residual disease, comorbidities, or other unmeasured factors is unclear. Third, women report worse quality of life for each of the measures that we examined. They report 2.3 more days of impaired physical or mental functioning each month than men. Similar results have been previously reported.20 21 Fourth, our results clearly demonstrate that asthma significantly affects quality of life among the elderly. These findings are consistent with previous findings.22 Fifth, some racial or ethnic differences in quality of life were observed among participants with asthma, thus suggesting health disparities. Sixth, the number of physically unhealthy days during the previous 30 days (physical functioning) appeared more strongly related to self-reported asthma than to the number of mentally unhealthy days during the previous 30 days (mental functioning). This is also consistent with findings from other studies.23
Asthma researchers have long recognized the value of measuring quality of life. Consequently, a fair number of adult24 25 26 27 28 and pediatric29 30 31 32 33 34 asthma-specific quality-of-life questionnaires have been developed and are routinely used in studies of self-management and pharmacologic treatment of asthma.35 Quality-of-life studies of parents or caretakers of patients with asthma have also been conducted.36 37 In addition, health-care providers have been urged to incorporate quality-of-life measures in their care of patients with asthma.38 Measuring quality of life in patients with asthma may help to distinguish the severity of the disease,39 and change in reported quality of life may correlate with change in the clinical status of patients.40 41 42 Furthermore, patients with diminished quality of life are more likely to use health-care services.43 44 45 46 47
Despite the impressive literature about asthma and quality of life, few population-based studies of the impact of asthma on quality of life have been conducted.10
Physical functioning scores from the SF-36 of 110 adult patients with asthma were lower than were population norms in the Netherlands.48
Among 5,580 health maintenance organization patients with asthma aged 14 to 65 years, the mean scores for eight subscales of functional status were lower than those reported by the general population in a separate survey performed 6 years earlier.49
Furthermore, the authors found significant decreases in functional status with increasing severity of asthma. In a British study, quality of life among 60 asthmatic patients aged
70 years was worse than that among control patients.23
Scores for mental health and social functioning were comparable to scores found in the general population. In a French study of participants aged 20 to 44 years, persons with asthma (21 persons with severe asthma and 77 persons with mild-to-moderate asthma) had lower scores on the SF-36 than control subjects without asthma.50
In a study of 3,001 Australians aged
15 years, participants with asthma reported significantly lower scores on several SF-36 scales.10
The authors concluded that asthma had a major negative impact on the health-related quality of life in the community and that its impact was similar to that of other chronic health conditions. Studies from New York State, Connecticut, and Los Angeles, CA that used the BRFSS questions also showed that people with asthma experienced worse quality of life than people without asthma.51
52
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Little research has apparently been conducted on health-related quality-of-life issues among Hispanic adults or non-Hispanic African American with asthma. Puerto Rican, Mexican-American, and Cuban- American populations differ markedly with regard to asthma prevalence54 and asthma mortality,55 as well as with regard to measures of functional limitation and self-reported health status.56 Taken together, these previous findings indicate that Hispanic subgroups may differ notably regarding quality of life and asthma. Unfortunately, the BRFSS at present does not allow examination of this issue.
In terms of race and ethnicity, at least two points are of note. First, compared with participants who never had asthma, Hispanic and non-Hispanic African-American participants with asthma had significantly worse quality of life. Second, both Hispanic and non-Hispanic African-American participants with asthma reported experiencing more physically unhealthy days, mentally unhealthy days, days with activity limitations, and physically or mentally unhealthy days than did non-Hispanic white participants with asthma. Hispanics reported the highest number of impaired physically or mentally unhealthy days of the four race or ethnic groups. In a previous study, 66 white and 46 African-American patients with asthma had similar scores for the physical and mental components of the SF-36.57 In another study, race was found to be an important predictor of worse quality of life among 50 participants with asthma.58
Several limitations deserve comment. The questions about self-reported asthma have not been tested for reliability or validity in the BRFSS. Other studies have suggested that the agreement between self-reported asthma and medical records is substantial, however.59 60 In published studies, the sensitivity of self-reported asthma ranges from 48 to 100% (mean 68%) when compared with a clinical diagnosis of asthma, and the specificity ranged from 78 to 100% (mean 94%).61 Because only two questions about asthma were included in the BRFSS questionnaire, we were unable to look at the associations between other issues specific to asthma, such as asthma severity, and quality of life.
Although BRFSS quality-of-life questions were developed for use in the general population rather than in populations of patients with specific conditions, generic quality-of-life questionnaires have been repeatedly used in studies of patients with asthma and found to be of value.23 44 48 62 63 64 As in many nonspecific health surveys, the number of questions on the BRFSS for any given health topic is severely limited. Although brief, the Centers For Disease Control and Prevention health-related quality-of-life questions used in the BRFSS were derived from key concepts measured in the SF-36 questionnaire, which has been extensively used by clinical researchers. An attractive feature of these questions is that they provide a measureperceived days of poor quality of lifethat is perhaps more intuitively appealing and easily interpretable than scores produced by other quality-of-life questionnaires.65
Telephone coverage bias is not likely to have affected these results because a very high proportion of US residents own telephones.66 For subgroups of the US population with very low telephone coverage, however, the associations between asthma and quality-of-life measurements may differ from those described in this article.
In conclusion, this is the largest study to have examined health-related quality-of-life measures related to self-reported asthma. Our results are consistent with previous smaller studies and confirm that people with asthma experience diminished health-related quality of life. Because poor quality of life has serious ramifications for patients and society, these data suggest that the treatment of persons with asthma should also consider ways to help these patients improve their quality of life. To better evaluate the public health burden of asthma, it is important to monitor quality-of-life issues to establish a more comprehensive picture of the impact of this health condition and its economic consequences. These data suggest that the BRFSS holds considerable promise as a useful surveillance tool and provides valuable information about an important aspect of the health of the increasing number of people with asthma in the United States.
| Footnotes |
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Received for publication April 9, 2002. Accepted for publication July 17, 2002.
| References |
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