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A national study of medical care expenditures for respiratory conditions

A national study of medical care expenditures for respiratory conditions
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  A national study of medical care expenditures for respiratoryconditions E. Yelin * ,# , L. Trupin # , M. Cisternas } , M. Eisner * , P. Katz # , P. Blanc * A national study of medical care expenditures for respiratory conditions. E. Yelin,L. Trupin, M. Cisternas, M. Eisner, P. Katz, P. Blanc. # ERS Journals Ltd 2002. ABSTRACT: This study was undertaken to estimate the magnitude of medical careexpenditures among persons with respiratory conditions in the USA in 1996, and theincrement in expenditures attributable to these conditions.The study data were derived from the 1996 Medical Expenditure Panel Survey, anational sample of 21,571 persons. Of the 21,571, 1,027 reported one or morerespiratory condition. After weighting, the individuals may represent about 12.1 millionpersons in the USA. All medical care expenditures of these individuals were tabulated,stratified by comorbidity status, and then compared to those among persons withnonrespiratory conditions or with no conditions. Regression techniques were then usedto estimate the increment of healthcare expenditures attributable to the respiratoryconditions.From a national total of $45.3 billion, medical care expenditures averaged $3,753among persons with respiratory conditions. Hospital stays comprised the largestcomponent (45%). The per capita increment in total expenditures attributable torespiratory conditions ranged from $1,003–2,588, from a national total ranging from$12.1–31.3 billion.The total medical care expenditure of persons with respiratory conditions wasestimated to be $45.3 billion, of which $12.1–31.3 billion represents an increment inexpenditures associated with the conditions themselves. Eur Respir J 2002; 19: 414–421. *Division of Occupational and Envi-ronmental Medicine,  # Division of Rheumatology, Dept of Medicine, Uni-versity of California and  } MGC DataServices, San Francisco, USA.Correspondence: E. YelinUCSF Box 0920San FranciscoCalifornia 94143-0920USAFax: 1 4154769030E-mail: yelin2@itsa.ucsf.eduKeywords: Cost of illnesseconomicsrespiratory conditionsReceived: September 16 2001Accepted after revision September 192001This study was supported by GrantNHLBI R01 HL56438. Cost of illness studies are a common method of documenting the impact of medical conditions. Inrecognition of the increased prevalence, severity, andmortality of chronic respiratory conditions in recentyears [1, 2], there have been a large number of studiesdocumenting the costs of specific upper and lowerrespiratory tract conditions, especially asthma andchronic obstructive pulmonary disease (COPD) [3–28].Although many of the studies in the literature arebased on clinical [12, 16, 19, 26] or local [20, 26],population-based data, a few integrate data fromseveral national surveys [4, 27–29]. Several studiesmake national estimates from the 1987 National Med-ical Expenditures Survey, a national, population-based survey [10, 11, 15]. However, none of thestudies used a national, population-based survey toestimate medical care expenditures for the entirerespiratory condition category, including chronicbronchitis, emphysema, asthma, and COPD, as wellas several less prevalent conditions. Moreover, priornational, population-based studies of specific diseaseentities [4, 10, 11, 15, 27–29] may be outdated becausethey are based on data that precede much of thegrowth in the prevalence of asthma and chronicbronchitis, two of the most common respiratoryconditions.The present study was designed to present morecontemporary national estimates of medical careexpenditures for the entire respiratory conditioncategory. Prior studies [13, 30, 31] predate thedevelopment of methods to estimate the incrementin expenditures specifically attributable to a condi-tion, methods which can provide more conservativeestimates of the economic impact of respiratoryconditions.The specific goals of the present study were to:1) provide estimates of all medical care expenditureson behalf of persons with chronic respiratory condi-tions in the USA in 1996; and 2) estimate the incre-ment in expenditures specifically attributable to therespiratory conditions among such persons. Methods Data Source The present study used data from the MedicalExpenditure Panel Survey (MEPS), a joint endeavourof the Agency for Health Care Research and Qualityand the National Centre for Health Statistics. MEPSis designed to provide data on healthcare use, medicalcare expenditures, sources of payment, and insurancecoverage for a representative sample of the non-institutionalized population of the USA. The fullMEPS data include survey responses from this sample Eur Respir J 2002; 19: 414–421DOI: 10.1183/09031936.02.00522001Printed in UK – all rights reservedCopyright  # ERS Journals Ltd 2002European Respiratory JournalISSN 0903-1936  of households (hereafter, MEPS-H), informationabout the specifics of their health plans provided bythe plans themselves, and a separate sample of nursinghome residents [32]. The MEPS-H sample derivesfrom the prior year 9 s National Health InterviewSurvey (NHIS) respondents, who are, in turn, derivedfrom a clustered, random sample of the civiliannoninstitutionalized population, with an oversampleof African-Americans and Hispanics. In the presentpaper, data from the first year of MEPS-H, 1996, wasused. To establish the MEPS-H, a subset of house-holds from the 1995 NHIS were targeted for inclusionin MEPS, 77.7% (10,639) of which were enrolled.These 10,639 households included 22,601 persons, of whom 21,571 provided data throughout 1996 (95.4%).MEPS-H data were collected through six roundsof interviews over a 2.5-yr period. The first threeinterviews, covering expenditures over an entire year,provided the data used in the analysis for this paper.The interviews were used to collect information onhealth status, healthcare utilization and expenditures,as well as basic demographic information. The healthstatus section elicited data on the specific medicalconditions each respondent self-reported. These werethen coded to three-digit levels using the InternationalClassifications of Diseases-ninth revision (ICD-9)system. Such self-reports may not perfectly conformto diagnoses made by physicians. The utilization andexpenditure sections elicited information on health-care episodes since the prior interview. The frequencyof interviews was designed to improve the reliability of responses.In the MEPS, expenditure data derive from acombination of the MEPS-H interviews and informa-tion provided by insurance plans. Expenditures inMEPS are defined as the actual expenditures for themedical care services used, regardless of the source of payment [32, 33]. In studies on medical care expen-ditures, the analyst studies the actual exchange of money which contrasts with studies on the costs of illness, in which costs are tabulated even if uncom-pensated care is provided on the assumption thatresources are being consumed regardless of payment.Because MEPS is based on expenditures rather thancosts, there are healthcare encounters for which noexpenditures are made.In an entirely fee-for-service system, all expendi-tures among respondents could be tracked. However,in many forms of managed care, charges are notrendered when services are provided and, hence, thereare no expenditures specific to medical care encoun-ters. Accordingly, in such instances, MEPS-H imputesexpenditures based on the charges incurred within thefee-for-service sector for similar services provided tosimilar individuals. AnalysesData partitions.  In the analyses for this report, esti-mates of the expenditures of persons with respira-tory conditions are presented. The specific conditionsincluded were ICD-9 codes 491 (chronic bronchitis),492 (emphysema), 493 (asthma), 494 (bronchiectasis),496 (chronic airway obstructive disease, not elsewhereclassified), 500 (coal worker 9 s pneumoconiosis), and501 (asbestosis). The entire MEPS-H data file was thenpartitioned into the following condition groups on thebasis of ICD-9 codes: persons with only respiratoryconditions, persons with both respiratory and non-respiratory chronic conditions, persons with onenonrespiratory condition, persons with two or morenonrespiratory chronic conditions, and persons withno chronic conditions. Owing to the sample size of theMEPS, some respiratory conditions were not reportedbyanyMEPSrespondent.Others,suchasCOPD,werereported by relatively few respondents, precludingreliable estimates of their national economic impact.For this report, chronic conditions were defined by theprotocol devised by H OFFMAN  et al.  [34]. General considerations.  BecauseMEPS-Hisbasedonatwo-stage cluster sample rather than a true randomsample of the noninstitutionalized population, it wasnecessary to weight the data to make inferences for theUSA population. In MEPS-H, the sampling weightsalso take into account nonresponses in the house-holds targeted for inclusion and omission amongrespondents,aftercompletionofthefirstinterview[35].Software was used to account for the cluster-samplingdesign in the calculation of the  SE  of parameters. Description of utilization and expenditures.  Inititially,the sizes of the five condition groups were enumerated(persons with respiratory conditions, persons withand without nonrespiratory conditions, persons withone, or more than one nonrespiratory chronic condi-tion, and persons with no chronic conditions). Thefrequency with which each major category of healthcare was used by persons in the conditiongroups was then shown, including ambulatory visits tophysicians and nonphysicians, prescription medica-tions, home-health days (days in which healthproviders assist in daily activities), and hospitaladmissions. Subsequently, medical care expendituresof persons in the condition groups (and withinthe respiratory condition group, for those with themost prevalent specific diseases, including chronicbronchitis, emphysema, and asthma) were estimatedby category of health services, and the distributionof total healthcare expenditures among persons withall forms of respiratory disease was shown. In theforegoing analysis, all expenditures among personsin the condition groups were tabulated, regardless of whether or not the condition in question accountedfor the expenditures. The results indicate those esti-mates with low statistical reliability (estimates with arelative standard error of  w 30%). Analysis of increment in healthcare expenditures.  Inorder to assess the incremental contribution of respiratory conditions to healthcare expenditures, aseries of regressions were estimated separately forpersons with and without respiratory conditions.Because the two demographic variables used in theseregressions (education and marital status) are notapplicable to children, data on these characteristics 415 MEDICAL COST OF RESPIRATORY CONDITIONS  were obtained from the adults in each child 9 s family.In addition, since missing values for any of theindependent variables in a regression will causeobservations to be deleted, the data was subset onlyto those observations with values present.This resultedin two and 311 observations being deleted fromthe respiratory and nonrespiratory categories, respec-tively. The characteristics of persons with respiratoryconditions were then substituted into the regres-sion models developed for those without respiratoryconditions. This technique allowed simulation of thelevel of expenditures that persons with respiratoryconditions would experience in the absence of theseconditions. The increment was then calculated asthe difference between the simulated amount and thepredicted expenditures from the respiratory group[36]. To make these calculations with respect toambulatory care, in-patient, and prescription drugexpenditures, the two-stage method outlined by D UAN et al.  [37] was followed. D UAN  et al.  [37] developedthis method because many persons have relatively lowhealth expenditures, or none, while a small proportionhave very high expenditures, primarily due to hospitaladmissions. In this method, logistic regression isused to estimate the probability that an individualhas any expenditures, followed by ordinary leastsquares regression to estimate the level of expendi-ture among those with expenditures.The incremental contribution of respiratory condi-tions to total expenditures was estimated by a four-stage model, using separate logistic procedures topredict the probability of any hospital and medicalexpenditures. Separate ordinary least squares proce-dures were estimated to predict the level of total costs(including ambulatory and in-patient care, prescrip-tion drugs, and a residual category that includedservices such as home healthcare and medical devices)among persons with and without hospitalizations.In the ordinary least squares regressions, a log trans-formation was used to account for the skeweddistribution of expenditures. In both the logisticand ordinary least squares procedures, the dependentvariable was regressed on indicator variables for thepresence or absence of respiratory conditions andthe following major chronic conditions: hypertension,other forms of heart disease, stroke, other neuro-logical conditions, diabetes, cancer, musculoskeletalconditions, and mental illness.In addition to the model including only theindicator variables for conditions, a separate modelwas estimated, which included the condition variablesand a count of chronic conditions. In the latter model,the parameter estimates indicated the magnitude of the effect of a condition after taking into account theextent of comorbidity. Models were also estimatedwhich, in addition to the condition indicator variables,controlled for demographic characteristics (age, bycategories; sex; White  versus  non-White race; Hispanicstatus; marital status; level of formal education),and overall health status (one item measurements of perceived physical and mental well-being [38, 39]singly and combined). The parameter estimate for therespiratory condition variable in the latter modelsindicated the magnitude of the effect of that conditionon expenditures, after taking into account the differ-ence between persons with and without respiratoryconditions in demographic characteristics and healthstatus.The mean expenditures controlling for the cova-riates described earlier were calculated by exponen-tiating the predicted values for each observation,multiplying the result by a  " smearing "  coefficient(the sum of the exponentiated residuals divided bythe sample size pooled from the respondents with andwithout respiratory conditions), and then averagingthe observations. Results Prevalence of respiratory conditions After applying the sampling weights, it was esti-mated that there were y 12.1 million persons (4.5% of the population) with at least one respiratory condi-tion. Of these, it was estimated that there were y 9.7million (3.6% of the entire population and 80.2% of all persons with respiratory conditions) with one ormore nonrespiratory conditions (table 1). In addition,it was estimated that there were 163.5 million persons Table 1.–Number and per cent of the noninstitutionalized population, by condition status, USA, 1996 (authors 9  analysis ofMedical Expenditures Panel Study) Condition status n (in millions) TotalpopulationPersons with respiratoryconditionsAll respiratory conditions 12.1 4.5 100.0Respiratory conditions only 2.4 0.9 19.8Respiratory and other chronic conditions 9.7 3.6 80.2Asthma 10.4 3.9 85.6All nonrespiratory conditions 163.5 60.8One nonrespiratory condition only 63.1 23.5Two or more nonrespiratory conditions 100.4 37.3No chronic/comorbid conditions 93.3 34.7Data are presented as % unless otherwise stated. Respiratory conditions included in the rubric are International Classificationof Diseases-ninth revision codes 491 (chronic bronchitis), 492 (emphysema), 493 (asthma), 494 (bronchiectasis), 496 (chronicairway obstruction, not elsewhere classified), 500 (coal worker 9 s pneumoconiosis) and 501 (asbestosis). Respondents may havehad more than one of the following respiratory conditions: chronic bronchitis, emphysema, and asthma.416  E. YELIN ET AL.  (60.8%) with nonrespiratory chronic conditions inthe absence of respiratory conditions and another93.3 million (34.7%) with no chronic conditions.Among the y 12.1 million persons estimated to haveone or more respiratory conditions,  y 10.4 millionwere estimated to have asthma (individuals, however,could report more than one respiratory condition). Description of utilization and costs Table 2 tabulates medical care utilization by con-dition group. A significantly larger proportion of persons with respiratory conditions reported ambula-tory physician visits, prescription medications filled,and hospital discharges than persons with nonrespira-tory conditions or those with no chronic condi-tions. In addition, a significantly larger proportionof persons with respiratory conditions reportedambulatory nonphysician visits and home healthcaredays than those with no chronic conditions but suchpersons did not differ from those with nonrespiratoryconditions in the proportion using medical care of thistype. Among those using each kind of service, personswith respiratory conditions had higher utilizationrates of ambulatory physician visits and prescriptionmedications filled than those with nonrespiratoryconditions. They also had higher utilization rates of each kind of service, other than home healthcare, thanpersons with no chronic conditions.Persons with all forms of respiratory conditionshad substantially larger average total medical careexpenditures than persons with nonrespiratorychronic conditions; $3,753  versus  $2,624, respectively(table 3). Persons with respiratory and nonrespiratoryconditions reported larger average total expendituresthan persons with two or more nonrespiratoryconditions ($4,465  versus  $3,443), but persons whoreported only having respiratory conditions hadaverage total expenditures less than two-thirds of those of persons with one nonrespiratory condition($843  versus  $1,321). Among all persons with respira-tory conditions, hospital stays accounted for 45% of total expenditures. Other large components includedphysician visits (18%) and prescriptions (17%). Totalexpenditures averaged $2,973 among all persons withasthma.Overall, persons with respiratory conditionsaccounted for $45.5 billion in annual expenditures,representing the equivalent of  y 0.6% of the GrossDomestic Product for the USA in 1996 [40]. However,all but $2.0 billion of the expenditures were frompersons with both respiratory and nonrespiratoryconditions.Table 4 shows the distribution of medical careexpenditures among persons with respiratory andnonrespiratory chronic conditions and among thosewith no chronic conditions. Among persons who onlyhad respiratory conditions, median annual medicalcare expenditures were only $189, and even at the75th percentile, these expenditures only reached $452.Among persons with both respiratory and nonrespira-tory chronic conditions, expenditure levels weremuch higher: median expenditures were $1,308 and Table 2.–Annual healthcare utilization (by type) of the noninstitutionalized population, by condition status, USA, 1996(authors 9  analysis of Medical Expenditures Panel Study) Kind of health service Condition status Among all persons% with anyAmong those using this serviceMean ¡ SE  MedianAmbulatory physician visitsRC 86.5* 7.0 ¡ 0.31* 5NRC 82.4* 5.7 ¡ 0.09* 3CC 43.3* 2.6 ¡ 0.07* 2Ambulatory nonphysician visitsRC 41.2 # 6.3 ¡ 0.63 # 2NRC 38.0 # 5.3 ¡ 0.20 # 2CC 11.7 # 2.7 ¡ 0.22 # 1Prescription medication filledRC 93.0* 21.0 ¡ 1.13* 10NRC 82.3* 13.4 ¡ 0.31* 6CC 35.0* 3.7 ¡ 0.23* 2Home healthcare daysRC 5.4 # 83.3 ¡ 20.00 28NRC 3.6 # 79.0 ¡ 5.42 28CC 0.6 # 46.4 ¡ 20.21 6Hospital dischargesRC 14.7* 1.6 ¡ 0.07 # 1NRC 9.3* 1.4 ¡ 0.03 # 1CC 2.6* 1.1 ¡ 0.04 # 1RC: all with respiratory conditions; NRC: all with nonrespiratory conditions; CC: all with no chronic conditions. Respiratoryconditions included in the rubric are International Classification of Diseases-ninth revision codes 491 (chronic bronchitis),492 (emphysema), 493 (asthma), 494 (bronchiectasis), 496 (chronic airway obstruction, not elsewhere classified), 500 (coalworker 9 s pneumoconiosis) and 501 (asbestosis). Estimates of the home health days among persons with no chronic conditionsare statistically unreliable (relative  SE  of  w 30%). *: p v 0.05 between the two condition groups, and between each group and theno condition group.  # : p v 0.05 between each condition group and the no condition group.417 MEDICAL COST OF RESPIRATORY CONDITIONS  expenditures at the 75th percentile were $4,253.Median medical care expenditures among personswith one or two or more nonrespiratory chronicconditions were $184 and $977, respectively. Thelatter figure is considerably lower than the $1,308expenditure of persons with respiratory and non-respiratory conditions. Analysis of the increment in expenditures The $45.5 billion in annual expenditures amongpersons with respiratory conditions was only partiallyattributable to the respiratory conditions themselves.A significant fraction was due to other chronicconditions and to acute and preventative care.Table 5 presents the results of several sets of analysesintended to calculate the magnitude of the incrementin medical care expenditures directly attributable torespiratory conditions. The results of the first set of analyses present estimates of the magnitude of theincrement in ambulatory and in-patient care, andprescription drugs and total expenditures attributableto respiratory conditions, when taking into accountthe other conditions that the MEPS respondentsreported. Respiratory conditions were responsiblefor annual per capita increments of $239 in ambula-tory care expenditures, $358 in prescription drugs,$616 in in-patient expenditures, and $1,583 in overallexpenditures (the latter figure is smaller than the sumof the prior three because persons with respiratoryconditions have a negative increment in the residualcategory, indicating lower expenditures).When the estimate of the increment in per capitatotal expenditures ($1,583) was multiplied by theestimated number of persons with respiratory condi-tions (12.1 million) the total increment amounted to y $19.2 billion a year. The $1,583 figure representedmore than two-fifths of the average total expendituresof $3,753 among persons with respiratory conditions(latter datum from table 3). The annual per capitaincrement in total expenditures actually increasedafter controlling for the total number of chronicconditions ($1,862) and demographic characteristics($2,588), but was slightly smaller when controlling forhealth status ($1,003). After controlling for all of thesesets of variables, the increment was $2,579 per capita.When the latter estimate was multiplied by theestimated number of persons with respiratory condi-tions, the total increment amounted to y $31.2 billion.However, even when the smallest estimate of the percapita increment ($1,003) was multiplied by theestimated number of persons with respiratory condi-tions, the total increment remained a substantial $12.1billion. Discussion Two kinds of estimates of the economic impact of respiratory conditions have been made. In the first,the magnitude and distribution of all medical careexpenditures among the estimated 12.1 million per-sons with respiratory conditions was recorded and the      T    a     b     l    e     3 .   –     E    s     t     i    m    a     t    e     d    a    n    n    u    a     l     h    e    a     l     t     h    c    a    r    e    e    x    p    e    n     d     i     t    u    r    e    s     (     b    y     t    y    p    e     )    o     f     t     h    e    n    o    n     i    n    s     t     i     t    u     t     i    o    n    a     l     i    z    e     d    p    o    p    u     l    a     t     i    o    n ,     b    y    c    o    n     d     i     t     i    o    n    s     t    a     t    u    s ,     U     S     A ,     1     9     9     6     (    a    u     t     h    o    r    s                            9 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      #      1     7     6     (     2     1     )     3     2     (     4     )     5     3     (     6     )     1     9     8     (     2     4     )       #      2     (     0     )     1     7     (     2     )       #      2 .     0     R   e   s   p     i   r   a    t   o   r   y   a   n     d   o    t     h   e   r   c     h   r   o   n     i   c   c   o   n     d     i    t     i   o   n   s     4 ,     4     6     5     2 ,     0     0     1     (     4     5     )     7     7     6     (     1     7     )     3     1     0     (     7     )     1     1     4     (     3     )     7     6     4     (     1     7     )     3     6     2     (     8     )     1     3     9     (     3     )     4     3 .     5     A   s    t     h   m   a     2 ,     9     7     3     1 ,     2     0     7     (     4     1     )     5     9     7     (     2     0     )     2     2     8     (     8     )     9     6     (     3     )     5     8     6     (     2     0     )     1     7     3     (     6     )     8     5     (     3     %     )     3     0 .     8     A     l     l   n   o   n   r   e   s   p     i   r   a    t   o   r   y   c   o   n     d     i    t     i   o   n   s     2 ,     6     2     4     1 ,     1     2     6     (     4     3     )     6     0     0     (     2     3     )     2     1     0     (     8     )     7     7     (     3     )     3     7     2     (     1     4     )     1     8     8     (     7     )     5     1     (     2     )     4     2     8 .     9     O   n   e   n   o   n   r   e   s   p     i   r   a    t   o   r   y   c   o   n     d     i    t     i   o   n     1 ,     3     2     1     7     4     1     (     5     6     )     2     7     8     (     2     1     )     8     3     (     6     )     6     1     (     5     )     1     1     4     (     9     )     2     9     (     2     )     1     5     (     1     %     )     8     3 .     4     T   w   o   o   r   m   o   r   e   n   o   n   r   e   s   p     i   r   a    t   o   r   y   c   o   n     d     i    t     i   o   n   s     3 ,     4     4     3     1 ,     3     6     8     (     4     0     )     8     0     1     (     2     3     )     2     9     0     (     8     )     8     7     (     3     )     5     3     5     (     1     6     )     2     8     9     (     8     )     7     3     (     2     )     3     4     5 .     6     N   o   c     h   r   o   n     i   c   c   o   n     d     i    t     i   o   n   s     3     6     5     1     3     7     (     3     8     )     1     1     3     (     3     1     )     3     4     (     9     )     3     3     (     9     )     2     6     (     7     )     1     1     (     3     )       #      9     (     3     )       #      3     4 .     0     T   o    t   a     l     1 ,     8     9     1     8     0     8     (     4     3     )     4     3     3     (     2     3     )     1     5     1     (     8     )     6     3     (     3     )     2     6     5     (     1     4     )     1     3     2     (     7     )     3     9     (     2     )     5     0     8 .     5     D   a    t   a   a   r   e   p   r   e   s   e   n    t   e     d   a   s   m   e   a   n     U     S     D   o     l     l   a   r   s     (     $     )   o   r     $     (     %     )   u   n     l   e   s   s   o    t     h   e   r   w     i   s   e   s    t   a    t   e     d .     E     R   :   e   m   e   r   g   e   n   c   y   r   o   o   m .       #    :   e   s    t     i   m   a    t   e   s   a   r   e   s    t   a    t     i   s    t     i   c   a     l     l   y   u   n   r   e     l     i   a     b     l   e     (   r   e     l   a    t     i   v   e      S     E    o     f      w      3     0     %     ) .     R   e   s   p     i   r   a    t   o   r   y   c   o   n     d     i    t     i   o   n   s     i   n   c     l   u     d   e     d     i   n    t     h   e   r   u     b   r     i   c   a   r   e     I   n    t   e   r   n   a    t     i   o   n   a     l     C     l   a   s   s     i     fi   c   a    t     i   o   n   s   o     f     D     i   s   e   a   s   e   s  -   n     i   n    t     h   r   e   v     i   s     i   o   n   c   o     d   e   s     4     9     1     (   c     h   r   o   n     i   c     b   r   o   n   c     h     i    t     i   s     ) ,     4     9     2     (   e   m   p     h   y   s   e   m   a     ) ,     4     9     3     (   a   s    t     h   m   a     ) ,     4     9     4     (     b   r   o   n   c     h     i   e   c    t   a   s     i   s     ) ,     4     9     6     (   c     h   r   o   n     i   c   a     i   r   w   a   y   o     b   s    t   r   u   c    t     i   o   n ,   n   o    t   e     l   s   e   w     h   e   r   e   c     l   a   s   s     i     fi   e     d     ) ,     5     0     0     (   c   o   a     l   w   o   r     k   e   r                            9    s   p   n   e   u   m   o   c   o   n     i   o   s     i   s     )   a   n     d     5     0     1     (   a   s     b   e   s    t   o   s     i   s     ) .     R   e   s   p   o   n     d   e   n    t   s   m   a   y     h   a   v   e   m   o   r   e    t     h   a   n   o   n   e   o     f    t     h   e     f   o     l     l   o   w     i   n   g   r   e   s   p     i   r   a    t   o   r   y   c   o   n     d     i    t     i   o   n   s   :   c     h   r   o   n     i   c     b   r   o   n   c     h     i    t     i   s ,   e   m   p     h   y   s   e   m   a ,   a   n     d   a   s    t     h   m   a .     T     h   e    t   o    t   a     l   n   a    t     i   o   n   a     l   c   o   s    t     i   n     b     i     l     l     i   o   n   s   w   a   s   c   a     l   c   u     l   a    t   e     d     b   y   m   u     l    t     i   p     l   y     i   n   g    t     h   e    t   o    t   a     l   o     f   a     l     l   s   e   r   v     i   c   e   s     (    t     h     i   s    t   a     b     l   e     )     b   y    t     h   e   p   r   e   v   a     l   e   n   c   e     i   n   m     i     l     l     i   o   n   s     (     f   r   o   m    t   a     b     l   e     1     ) . 418  E. YELIN ET AL.
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