Williams, Setareh A. PhD; Wagner, Samuel PhD; Kannan, Hema MPH; Bolge, Susan C. PhD
Asthma is the third most prevalent chronic condition in the U.S. with increasing prevalence.1,2 The lack of asthma control is evidenced by the high occurrence of attacks among currently diagnosed asthmatic patients with 57% (11.7 of 20 million asthma patients in the U.S.) reporting attacks annually.3
Not only is asthma prevalent, it is also the fourth most costly disease in the United States in terms of per capita direct costs with a total annual cost estimate of $12.7 billion.1,4 Emergency department (ED) visits, hospitalizations, and death account for one third of the direct costs associated with asthma.5 In 2004, 497,000 hospitalizations and 1.8 million ED visits were attributed to asthma.3 The burden of asthma in the United States has not been reduced despite the availability of effective therapies. Although hospital discharge rates for asthma have declined overall from 1988 to 2002, hospitalization rates have remained high for women, children, elderly, and blacks.3 Patients with moderate-to-severe asthma are the major cost drivers, as they have significantly more uncontrolled events leading to hospitalizations, ED visits, clinic visits and consequently a higher total treatment costs than those with mild asthma.6
In addition to the direct cost of treatment, uncontrolled asthma impacts productivity and as such is a burden to US employers and health care payers.7 Indirect costs, such as work productivity and quality of life, for patients suffering from severe asthma are three times higher than costs for patients with moderate asthma and five times higher than costs for mild asthma sufferers.8
Optimal control of asthma with appropriate controller medications plays a pivotal role in alleviating the preventable cost of asthma care. Despite the evidence indicating the importance of asthma control, the availability of guidelines for proper management, patient-reported screening tools such as the Asthma Control Test (ACT), and the development of effective medications, some studies indicate that a high proportion of asthma patients receiving asthma medications remain symptomatic or uncontrolled.9
Although some evidence does exist in the literature regarding the impact of asthma control on health outcomes, the impact on direct and indirect costs of treatment has not been fully established. Studies conducted in the past have recruited participants from specific health care settings.7,10 The objective of this study is to determine the impact of asthma control on health resource utilization, health-related quality of life (HRQL), work productivity and activity impairment (WPAI) among a representative sample of the general US population. Based on reviews of existing literature on the effects of asthma control, we hypothesize that asthma control will be associated with better patient reported outcomes.
Data were obtained from the 2006 U.S. National Health and Wellness Survey (NHWS), a cross-sectional survey of the health care attitudes, behaviors, disease status, treatment choices, and outcomes of adults aged 18 and older.11–13 NHWS is conducted annually by Consumer Health Sciences (Princeton, NJ). The NHWS study protocol and questionnaire were reviewed and approved by the Essex IRB (Lebanon, NJ) and are HIPAA (Health Insurance Portability and Accountability Act) compliant.
The NHWS sample was identified through an Internet consumer panel and was stratified to reflect the gender, age, and racial distribution of the total U.S. adult population.14 Data were collected from respondents between March and September of 2006 through a self-administered, Internet-based questionnaire. Respondents were included in the current analyses if they self-reported physician diagnosed asthma and had experienced asthma symptoms in the past 12 months.
Asthma control during the 4 weeks preceding the survey was evaluated using the ACT, a validated instrument for assessment of asthma control in patients 12 years of age and older. The ACT has been used in multiple published studies and is supported by the American Lung Association.15,16 Final scores can range from 5 (poor control) to 25 (total asthma control).17,18 Controlled asthma was defined as an ACT score of 20 or more, and uncontrolled asthma was defined as an ACT score of 19 or less.15,16
Comorbid conditions were assessed using an adaptation of the Charlson Comorbidity Index.19 Conditions in the NHWS that were most comparable to the conditions in the Charlson Comorbidity Index were assigned weights. These weights were then summed for all conditions experienced by each respondent, yielding a measure of comorbidity for each respondent. The conditions used in the adaptation and their associated weights are summarized in Table 1.
HRQL was assessed using the Short-Form Health Survey (SF-8, Medical Outcomes Study), a generic measure of health status based on the SF-36.20 The SF-8 yields a physical component summary score and a mental component summary score. The summary scores are normalized to a mean of 50 and standard deviation of 10 for the U.S. adult population.20 Although a five point change in the SF-36 score, and by extension in the SF-8, has been considered to be a clinically meaningful difference, a recent reevaluation of existing HRQL literature concluded that a 3 to 5 point difference in scores is considered to be clinically meaningful for the SF-36.20,21
Work productivity loss and activity impairment for the previous 7 days were assessed using the WPAI questionnaire.22 Four metrics are computed from the WPAI: absenteeism (work time missed due to health problems), presenteeism (impairment at work or reduced effectiveness while working), overall work productivity loss (combination of absenteeism and presenteeism), and activity impairment due to health. These metrics are expressed as percent impairment with higher values indicating a greater proportion of impairment in work (less productivity) or activities.22,23 Although clinically meaningful differences have not been established for the WPAI measures, algorithms have been developed and applied in other studies to determine the hours per week of incremental work productivity loss due to health problems.24
Finally, self-reported health care resource utilization was assessed for the past 6 months. Five types of resource utilization were included in the analysis: number of ED visits, number of days hospitalized, number of visits to all medical providers, number of primary care provider visits, and number of visits to respiratory specialists.
Demographic profiles, comorbid conditions, and outcomes were compared for uncontrolled asthma sufferers and controlled asthma sufferers at the bivariate level. Significant differences were tested using the χ2 test for categorical variables and t tests for continuous variables. All bivariate analyses were two tailed (α = 0.05).
Linear regression models were developed to assess the independent effects of asthma control (controlled vs uncontrolled) on outcomes. Separate models were developed for each of the following outcome variables: HRQL, work productivity/activity impairment. Poisson regression models were developed for the resource utilization metrics, because they were counts of visits. Over dispersion was corrected by applying the Pearson χ2 correction in these models. Potential confounders adjusted for all the models included gender, age, race, marital status, education, and the adapted Charlson Comorbidity Index. Although analyses including HRQL, activity impairment, and health care resource utilization were evaluated for all asthma sufferers, measures of lost work productivity (absenteeism, presenteeism, and overall work impairment) were evaluated only for asthma sufferers who were employed fulltime at the time of the survey.
Of the 62,833 respondents who completed the 2006 U.S. NHWS, 5877 (9.4%) reported experiencing asthma in the past 12 months. Of these, 5679 (9.0%) respondents also reported that their asthma was diagnosed by a physician. On the basis of ACT assessment 2767 (48.7% of asthma sufferers) respondents were categorized as patients with uncontrolled asthma and 2912 (51.3% of asthma sufferers) were classified as patients with controlled asthma.
Compared to patients with uncontrolled asthma, patients with controlled asthma were significantly younger (43.9 vs 48.6; P < 0.001), more likely to be married (76.4% vs 67.5%, P < 0.001), and more likely to have a college degree (38.8% vs 26.1%; P < 0.001). Gender and racial distributions were comparable between patients with controlled and patients with uncontrolled asthma. Of those with controlled asthma, the average Charlson Index score was 0.45, which was significantly lower than the average Charlson Index score of 1.13 for patients with uncontrolled asthma (Table 2).
Effects of Asthma Control on Health Outcomes
In the current study, uncontrolled asthma appears to be negatively correlated with patients’ HRQL assessed by the SF-8. The average SF-8 physical component summary score for patients with uncontrolled asthma was 38.9 (vs 46.88 for controlled patients, P < 0.001) and the average SF-8 mental component summary score was 43.7 (vs 48.1, P < 0.001). These numbers were not only significantly lower than scores for patients with controlled asthma, but they were also notably lower than the normative means of 50 for the U.S. adult population (Table 3). Adjusting for demographics and comorbidity, individuals with controlled asthma had SF-8 physical component summary scores that were 5.3 points higher (P < 0.001) and SF-8 mental component summary scores that were 3.9 points higher (P < 0.001) than patients with uncontrolled asthma (Table 4), indicating the significant association between asthma control and patient HRQL.
Significant associations were also noted for work productivity loss. Patients with controlled asthma, who were employed full-time, experienced substantially less overall work impairment than patients with uncontrolled asthma (15.4% vs 27.6%, P < 0.001). Lower levels of absenteeism (4.7% vs 10.4%) and presenteeism (18.9% vs 34.3%) (were also noted among patients with controlled asthma, respectively) in comparison to patients with uncontrolled asthma (Table 3). Adjusting for the effects of demographics and comorbidity, patients with controlled asthma continue to experience less impairment at work. Patients with controlled asthma had 4.1% lower productivity impairment due to absenteeism, 13.3% lower productivity impairment while working (presenteeism), and 10.8% lower overall work productivity impairment than patients with uncontrolled asthma (Table 4).
Further, patients with controlled asthma experienced significantly less activity impairment than uncontrolled asthma sufferers (29.0% vs 51.2% activity impairment; P < 0.001) (Table 3). Adjusting for demographics and comorbidity, asthma control was associated with a 16.4% reduction in activity impairment among patients with asthma (Table 4).
The impact of asthma control was not limited to work productivity metrics. Patients with controlled asthma also had decreased levels of resource utilization. In bivariate analysis, patients with uncontrolled asthma had nearly three times as many ED visits and days hospitalized, as well as significantly higher provider visits than patients with controlled asthma (Table 3). Adjusting for demographics and comorbidity, patients with controlled asthma had 56% fewer ED visits, 55% fewer hospital days, and 24% fewer visits to medical providers over a 6-month period compared to patients with uncontrolled asthma (Table 5).
Asthma control remains an important issue as indicated by the high rates of attacks and resource utilization among asthmatics.3 Treatment guidelines and screening tools such as the ACT have been created to assist physicians as well as patients with monitoring and management of asthma control.17 Although the overall burden of illness associated with asthma has been well documented in the literature, the direct and indirect costs associated with uncontrolled asthma have only recently started to gain prominence.7,10 This is especially pertinent considering the progress made with therapeutic agents.2 Some research has been conducted to examine the impact of uncontrolled asthma with results indicating negative outcomes. Sullivan et al7 studied individuals treated by subspecialists for severe or difficult to treat asthma in a naturalistic setting. They noted that controlled asthmatics had fewer school/work absences as well as less health care resource utilization than patients with uncontrolled asthma.7 A study by Vollmer et al,10 also noted increased resource utilization and decreased HRQL among individuals with decreasing levels of asthma control. Results from the TENOR (The Epidemiology and Natural History of Asthma: Outcomes and Treatment Regimens) study indicate that uncontrolled asthma is the largest contributor to the burden of illness associated with this condition.25
The current study is comprised of a potentially healthier sample of asthma patients in a non-health care setting, but confirms results reported in earlier studies among patients in health care settings.7,10 This study’s results indicate that asthma control has a strong positive effect on HRQL. After adjusting for potential confounders, the 5.3 point effect of asthma control on physical summary score and the 3.9 point effect of asthma control on mental summary score have meaningful clinical implications. Although HRQL is important in and of itself as an outcome variable, it has also been noted to be a significant predictor of resource utilization, particular ED visits and medication utilization.17 Asthma specific resource utilization has been associated with patients’ self-report of HRQL in addition to asthma severity.7 Furthermore, HRQL was found to be correlated with ED visits and use of medications.17 Asthma control and adherence with asthma medication have been linked to improved health outcomes including HRQL.5,26 Thus, the results of the current study indicating that patients with uncontrolled asthma are more likely to have lower HRQL scores assessed by the SF-8 may be indicative of these patients also being at increased risk for ED admissions. This presents an opportunity not only for early identification but also for intervention as well.
Lack of asthma control is also correlated with increased indirect costs associated with work impairment. The overall work productivity loss experienced by patients with controlled asthma in the current study was 11% lower than that experienced by patients with uncontrolled asthma. This 11% translates to a gain of 4.4 hours in overall work productivity during a 40 hour workweeks. Assuming a total of 52 workweeks in a year, this yields 229 hours or 6 weeks of productivity per year gained for each patient with controlled asthma.24 The impact of this productivity gain could be significant if projected to the total number uncontrolled patients in the US. The anonymous nature of the NHWS as opposed to employer-sponsored surveys enables an open forum for patients to discuss factors driving productivity. Although analyses of existing databases can be used to determine rates of absenteeism, issues such as presenteeism and overall productivity loss are most informative from the patient perspective.
Asthma control is associated with a decrease in health care resource utilization as well. Controlled patients were half as likely to be hospitalized or visit an ED as uncontrolled patients. Similarly, they were also less likely to use medical providers. Similar associations between increases in resource utilization with decreasing levels of asthma control have been noted previously in literature.10 Resource utilization metrics such as these are known to be significant drivers of direct costs associated with asthma.5
The current study results should be interpreted within the context of several limitations. First, the subject recruitment and selection based on an Internet panel survey could potentially limit the generalizability of the study results; however, estimates from the U.S. Census Bureau indicate that 70% of the U.S. population does have Internet access.27 In addition, the NHWS asthma prevalence estimates were compared with the National Health Interview Survey’s (NHIS) prevalence estimate for asthma to assess the representativeness ofthis Internet sample. The prevalence of diagnosed asthma in the 2006 US NHWS survey (9.2%) is comparable to estimates reported by the NHIS in 2006 (7.3%). Another limitation is that the data were based on patient self-reported; however, the accuracy of patient self-report of medical diagnosis has been assessed and established, especially for chronic conditions.28 The current study is cross-sectional in nature and no causality can be established between the variables of interest. However, results of this analysis may be hypothesis generating for expanded studies. Asthma control was dichotomized in this analysis. Although this provides an overview of the impact of control, future analyses looking at asthma control as a continuous variable might provide further insight into the incremental benefits of levels of control. Finally, although the NHWS captures number of days hospitalized, ED visits, and medical provider visits, this information is all cause and not asthma specific.
Findings from this analysis add to the body of evidence linking asthma control to overall burden of disease. Increased awareness of the impact of asthma control may benefit employers as well as health care payers because preventive measures can be taken to reduce the number of asthma attacks. Asthma control consists of various factors including impact of symptoms on activities and daily life, use of medications, level of perceived control. These individual factors may have differential impact on outcomes to fully understand the experience of asthmatic patients. To fully understand the experience of asthmatics, individual factors affecting asthma control should be studied in the future. The use of screening tools, such as the ACT, to identify at risk patients may potentially lead to better management and decreased total direct and indirect asthma treatment costs. Although barriers to control have been identified in previous literature, stronger efforts in patient education and implementation of other programs to overcome these barriers are needed to achieve this goal.29
Supported by AstraZeneca LP, DE.
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