Air Pollution and the Development of Posttransplant Chronic Lung Allograft Dysfunction

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1 American Journal of Transplantation 2014; 14: Wiley Periodicals Inc. C Copyright 2014 The American Society of Transplantation and the American Society of Transplant Surgeons doi: /ajt Air Pollution and the Development of Posttransplant Chronic Lung Allograft Dysfunction S. Bhinder 1, H. Chen 2,3,4,M.Sato 5, R. Copes 2,4, G. J. Evans 6, C.-W. Chow 1,4,6 and L. G. Singer 1, * 1 Department of Medicine, University of Toronto, Toronto, Ontario, Canada 2 Public Health Ontario, Toronto, Ontario, Canada 3 Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada 4 Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada 5 Thoracic Surgery, Kyoto University, Kyoto-city, Kyoto, Japan 6 Department of Chemical Engineering and Applied Chemistry, Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, Toronto, Ontario, Canada Corresponding author: Lianne G. Singer, lianne.singer@uhn.ca Chronic lung allograft dysfunction (CLAD) is the leading cause of mortality following lung transplantation. We conducted a retrospective cohort study including 397 bilateral lung recipients transplanted in from 1996 to 2009 to determine the association between ambient air pollution, CLAD and mortality. Pollution exposure was assessed using satellite-based estimates of nitrogen dioxide, distance to major roadway and total length of roadways around a patient s home. Cumulative exposures to ozone and particulate matter were estimated from concentrations measured at fixed-site stations near patients homes using inverse distance weighted interpolation. Cox proportional hazards models were used to estimate the associations of CLAD with air pollution exposure, adjusting for various individual and neighborhood characteristics. During the follow-up, 185 patients developed CLAD (47%) and 101 patients died (25%). Fifty-four deaths (53%) were due to CLAD. We observed an association between CLAD development and road density within 200 m of a patient s home (HR 1.30 [95% CI ]). Although based on a subgroup of 14 patients, living within 100 m of a highway was associated with a high risk for developing CLAD (HR 4.91 [95% CI 2.22, 10.87]). These data suggest that exposure to traffic-related air pollution is associated with development of CLAD among lung transplant recipients. Abbreviations: CF, cystic fibrosis; CI, 95% confidence interval; CLAD, chronic lung allograft dysfunction; COPD, chronic obstructive pulmonary disease; DOMI- NO, Dutch OMI NO 2 ; EOS, Earth Observing System; FEV 1, forced expiratory volume in 1 s; HR, hazard ratio; IPF, idiopathic pulmonary fibrosis; IQR, interquartile range; NAPS, National Air Pollution Surveillance; NO 2, nitrogen dioxide; O 3, ozone; OMI, Ozone Monitoring Instrument; PM 2.5, particles with aerodynamic diameter <2.5 mm; TRAP, traffic-related air pollution Received 24 October 2013, revised 25 June 2014 and accepted for publication 29 June 2014 Introduction/Background Chronic lung allograft dysfunction (CLAD) is the leading cause of graft failure and mortality for transplant recipients, accounting for the poor median survival of lung transplant recipients of 5.6 years (1). CLAD is defined as a sustained loss of forced expiratory volume in 1 s (FEV 1 ) of greater than 20% from baseline in the absence of identifiable etiologies, such as infection, acute rejection or anastomotic complications (2). Beyond the first year posttransplant, CLAD accounts for over 25% of recipient deaths (1). The incidence of CLAD approaches 50% within 5 years of lung transplantation, and once diagnosed, median survival is only 3 years (1,3,4). CLAD is postulated to be the end result of multiple alloimmune and nonalloimmune factors that lead to chronic inflammation and lung injury, including primary graft dysfunction (5), alloantibodies (6), acute rejection (7), infections (8 10) and gastroesophageal reflux (11,12). It is plausible that repeated airway injury from exposure to traffic-associated air pollution could contribute to the development of CLAD. Several studies have shown associations between chronic exposure to traffic-related air pollution (TRAP) and increased risk of mortality from cardiovascular disease (13 15), and the incidence and exacerbations of asthma and chronic obstructive pulmonary disease (COPD) in Canadian cities (16 19). Chronic exposure to TRAP has been implicated in impairing lung development in children (18). In a cohort study of lung transplant recipients in Belgium, living close to a major roadway, a marker for TRAP exposure, was associated with the development of CLAD 2749

2 Bhinder et al and an increased risk of mortality (20). Identification of a relationship between TRAP and outcomes following transplantation in a geographically distinct cohort of lung transplant recipients would further support the validity of this proposed association, thus allowing for further study into underlying mechanisms toward potential interventions for decreasing allograft dysfunction and mortality. To address this question, we performed a retrospective cohort study of 397 patients who underwent bilateral transplantation in the Toronto Lung Transplant Program. Methods Patients The cohort consisted of all bilateral lung transplant recipients from 1996 to 2009 who were permanent residents of Ontario, Canada, at the time of transplantation, survived more than 3 months posttransplant and had full pulmonary function data. Outcome measures Patients had FEV 1 measurements weekly to monthly for at least the first 2 years posttransplant, and subsequently every 1 to 3 months thereafter. Baseline FEV 1 was determined as an average of the two best FEV 1 values posttransplant that were taken at minimum 3 weeks apart (26). CLAD was defined as an irreversible decline in FEV 1 to less than 80% of baseline, measured on two separate occasions at least 3 weeks apart (2). Irreversibility was determined after appropriate treatment for infection, rejection or both. The first date of an irreversible decline in FEV 1 was recorded as the date of onset for CLAD. Deaths were reported directly to the Lung Transplant Program by the patient s most responsible physician, family or both. Cause of death was determined by chart review, discussion with most responsible physician, death certificate, postmortem examination or a combination of the foregoing. Calculations of overall and post-clad survival were based on start dates of transplant and date of CLAD diagnosis, respectively, and end dates of April 30, Exposure assessment We assessed long-term exposure to TRAP using two metrics of distance from major traffic roads (highways, primary urban roads and arterial roads). First, we computed the shortest distances between the patients residential addresses at the time of transplantation and major traffic roads. Distances were categorized as 0 100, , and >1000 m. Second, we calculated the total length of major roads that fell within circular buffer regions of a series of radii (200, 300, 500 and 1000 m) from the patients home addresses. These two metrics have been used as surrogates of exposure to TRAP in epidemiological studies of chronic effects of air pollution (13,14,21,22). We estimated exposure to nitrogen dioxide (NO 2 ) at subjects homes using satellite-based estimates of surface concentrations of NO 2 (23). The satellite-based concentrations were derived using data from the Ozone Monitoring Instrument (OMI) onboard the Earth Observing System (EOS) Aura satellite, which passes over Ontario near midday each day. Variation in annually averaged ambient NO 2 in the province of Ontario is primarily spatial in nature rather than temporal (13); thus, it is valid to use mean NO 2 estimates from 2005 to 2009 to characterize NO 2 exposure over our retrospective cohort period. This inferred NO 2 exposure was expressed in terms of the interquartile range (IQR) of the 5-year average vertical column density ( molecules/cm 2 ). Values for days without excessive cloud cover were re-gridded onto grid squares to yield exposure estimates with a spatial resolution of 10 km 10 km. The OMI data were converted to vertical column densities through the Dutch OMI NO 2 (DOMINO) Product provided by the Tropospheric Emissions Monitoring Internet Service ( Exposure to fine particulate matter (particles with aerodynamic diameter <2.5 mm [PM 2.5 ]) and ozone (O 3 ) at the patient s home were determined using measured concentrations at nearby National Air Pollution Surveillance (NAPS) fixed-site monitoring stations where concentrations were measured for the entire study period (24,25). Air quality standards in Canada are based on PM 2.5 rather than PM 10, thus much more extensive PM 2.5 than PM 10 data were available for Ontario over the study period. Long-term exposures were calculated by averaging daily concentrations of PM 2.5 and O 3 between 1996 and 2009 and assigned to subjects homes using inverse distance weighted interpolation method. A subset of the patients living residing within 10 km of a NAPS monitoring station was also examined. Covariates From patient s charts and the Lung Transplant Program Research Database, we extracted the age, gender, clinical indication for transplant, type of transplant (double-lung vs. heart-lung), spirometry, diagnosis of CLAD, chronic azithromycin use for greater than 1 month, and incidence of death for each lung allograft recipient. Determination of donor age and gender was extracted from our database based on data provided by the Trillium Gift of Life Network. We created three contextual variables: (1) proportion of population aged >15 years with less than high school education; (2) unemployment rate and (3) mean household income from the Canadian Census in 2001 using census tracts. In addition, we created a variable of urban/rural residence. Urban areas are those continuously built-up areas having a population of >1000 and a population density of 400 or more per square kilometer based on the 2001 census. To control for large-scale spatial patterns in CLAD that might be caused by factors other than pollution, we created an indicator variable classifying Ontario into southern and northern regions according to the 14 Local Health Integrated Networks of Ontario. Statistical methods We used a stratified Cox proportional hazards model with strata defined as region (south/north). Follow-up time was measured in days, calculated from the date of transplantation through the last date of the pulmonary function test or the date of last clinical visit, whichever came later. CLAD and death were examined separately as outcomes. For CLAD analyses, subjects were censored if they died without CLAD. In separate Cox proportional hazards models, we modeled exposure to TRAP as: (1) proximity to roadways (0 100, and m), with the cohort residing >1000 m from a major road or highway considered the reference group for comparison and assigned a hazard ratio (HR) of 1; (2) lengths of major roads within 200, 300, 500 and 1000 m radii from the patient s home addresses; (3) satellite-based estimates of NO 2 and (4) annual concentrations of PM 2.5 and O 3 averaged over the period 1996 to In all models, we adjusted for age at baseline, sex, pretransplant diagnosis, age and gender of donor, sex matching between donor and recipient, year of transplantation, rural/urban residency, as well as neighborhood-level unemployment, education and average household income. Because 2750 American Journal of Transplantation 2014; 14:

3 Pollution and Chronic Lung Allograft Dysfunction azithromycin was generally prescribed in response to a drop in lung function, we did not adjust our analyses for azithromycin use. With the exception of proximity to major roads, we reported adjusted HR and 95% confidence interval (CI) for other exposure metrics per increment of IQR. For all the Cox models, we tested deviations from the proportional hazards assumption by assessing whether the cross-product of each variable with the natural logarithm of the time variable was statistically important. We also investigated the presence of effect modification by age, sex, sex-matching and rural/urban residency. As a sensitivity analysis, we restricted analysis to subjects who lived within 10 km of monitoring stations and excluded subjects whose residential addresses did not contain any major road within radii of 200, 300, 500 and 1000 m, respectively. We further adjusted for an additional neighborhoodlevel variables and neighborhood percentage of landed immigrants. Ethics approval Our study was approved by the Research Ethics Board of the University Health Network. Results Of 495 subjects undergoing double-lung transplant during the inclusion period, 397 were included in the study. Reasons for exclusion included: permanent home address outside of Ontario (n ¼ 83), unable to geocode permanent home address (6) and missing demographic data (9). Baseline cohort characteristics for the 397 patients are presented in Table 1. The majority of patients were Table 1: Study subjects Characteristics N % Recipient age (mean SD), years Donor age (mean SD), years Transplant indication COPD CF IPF Pulmonary arterial hypertension 19 5 Bronchiectasis 18 4 Other Developed CLAD Death Cause of death CLAD Bacterial sepsis 9 9 Cancer Bacterial pneumonia 4 4 Liver failure 3 3 Other Azithromycin use in patients with CLAD Azithromycin use in patients without CLAD Survival (mean SD), days Overall (n ¼ 421) After CLAD diagnosis (n ¼ 173) CF, cystic fibrosis; CLAD, chronic lung allograft dysfunction; COPD, chronic obstructive pulmonary disease; IPF, idiopathic pulmonary fibrosis. American Journal of Transplantation 2014; 14: transplanted for COPD, cystic fibrosis (CF) and idiopathic pulmonary fibrosis (IPF). During the follow-up period, 47% of transplant recipients developed CLAD and 25% died. CLAD was the cause of death for 53% of transplant recipients. Azithromycin was prescribed for 214 patients (54%) and was more frequently prescribed for those with CLAD than without (81% vs. 30%, respectively). Most of the non-clad patients were prescribed azithromycin after drops in FEV 1 of less than 20% which did not meet CLAD criteria. Among patients with CLAD, 69% (104/150) began azithromycin after CLAD diagnosis. No significant associations were found between the development of CLAD with increased mean annual concentrations of PM 2.5,O 3 or NO 2 (Table 2). No significant, progressive increase in risk of developing CLAD was observed based on distance to the closest major roadway alone. The relationship between road distance as a continuous variable and CLAD is shown in Figure S1. There was a significant increased risk for development of CLAD, based on 14 patients, for patients living within 100 m of a major highway (HR 4.91; 95% CI ). Also, an increased roadway density within 200 m of a patient s home was associated with an increased risk for development of CLAD (HR 1.30; 95% CI ). The estimates of associations did not change appreciably in the sensitivity analyses (Table 3). Increased density of roadways, including at least one major road, within a 500, 300 and 200 m radius around patients homes was associated with increased risk for development of CLAD: HR 1.27 (95% CI ), HR 1.36 (95% CI ) and HR 1.22 (95% CI ), respectively. For 243 patients residing within 10 km of a NAPS monitoring site, increased long-term exposure to O 3 and PM 2.5 was also not associated with an increased risk of developing CLAD. None of the direct measurements of ambient pollution exposure were associated with an increased risk of mortality. No increase in mortality for lung transplant recipients was seen using metrics of roadways density or distance to major roads or highways (Table 4). Covariates of age, gender, donor recipient sex matching and rurality were not associated with development of CLAD (Table 5). As a sensitivity analysis, we further adjusted for an additional neighborhood-level variables and neighborhood percentage of landed immigrants and found that effect estimate for the association between road traffic within 200 m buffer and CLAD remained virtually unchanged (Table 6). Previous studies in Canada have shown that percentage of landed immigrants is an important predictor of economic deprivation. In addition, we repeated this analysis for several other metrics of road density as well as distance, and we observed similar results (data not shown). 2751

4 Bhinder et al Table 2: Hazard ratios (HR) and 95% confidence intervals (95% CI) for the associations of CLAD with different metrics of exposure for ambient air pollution in Ontario, among persons who received bilateral lung transplantation between 1996 and 2009 unadjusted and adjusted for ambient PM 2.5 Exposure metrics subjects CLAD unadjusted CLAD adjusted HR 95% CI HR 95% CI Annual concentration of PM 2.5 averaged between 1996 and , , assigned at residential addresses of all subjects (per IQR increment) Annual concentration of O 3 average between , , , 2.47 assigned at residential addresses of all subjects (in IQR) Remote sensed NO 2 for (IQR) , , 2.40 Density of major roads within 200 m buffer of residential , , 1.58 Density of major roads within 300 m buffer of residential , , 1.48 Density of major roads within 500 m buffer of residential , , 148 Density of major roads within 1000 m buffer of residential , , 1.43 Distance to major roads <100 m , , m , , m , , 3.65 >1000 m Distance to highways <100 m , , m , , m , , 1.57 >1000 m CLAD, chronic lung allograft dysfunction; IQR, interquartile range; NO 2, nitrogen dioxide; O 3, ozone; PM 2.5, particles with aerodynamic diameter < 2.5 mm. 1 Reference cohort for hazard ratio calculation assigned a HR value of 1. Discussion To the best of our knowledge, we are the second group to investigate an association between surrogates of TRAP exposure and lung transplant outcomes of CLAD and mortality. In confirming this association in a distinct cohort with very different patterns of traffic population exposure, our study strengthens and extends the evidence for the reported association between ambient pollution and chronic allograft dysfunction. The study by Nawrot et al (20) examined the impact of the proximity of a patient s home to the nearest major road on CLAD and mortality. For a cohort of 288 lung transplant Table 3: Sensitivity analysis of the associations between CLAD and different metrics of exposure for ambient air pollution in Ontario, among persons who received bilateral lung transplantation between 1996 and 2009 Sensitivity analyses subjects HR CLAD 95% CI Annual concentration of PM 2.5 averaged between , assigned at residential , 3.46 address within 10 km of monitoring stations (in IQR) Annual concentration of O 3 average between , assigned at residential address , within 10 km of monitoring stations (in IQR) Restricted to subjects whose residential address had traffic density of >0 for major roads Within 200 m buffer (per IQR increment) , 1.41 Within 300 m buffer (IQR) , 1.61 Within 500 m buffer (IQR) , 1.53 Within 1000 m buffer (IQR) , 1.38 CI, 95% confidence interval; CLAD, chronic lung allograft dysfunction; HR, hazard ratio; IQR, interquartile range; O 3, ozone; PM 2.5, particles with aerodynamic diameter <2.5 mm American Journal of Transplantation 2014; 14:

5 Pollution and Chronic Lung Allograft Dysfunction Table 4: Hazard ratios (HR) and 95% confidence intervals (95% CI) for the associations of all-cause mortality with various metrics of road density and distance from major roads and highways, among individuals who received bilateral lung transplantation in Ontario between 1996 and 2009 Exposure metrics events Hazard ratio Death 95% CI Density of major roads within , m buffer of residential Density of major roads within , m buffer of residential Density of major roads within , m buffer of residential Density of major roads within 1000 m buffer of residential , 1.45 Distance to major roads and highways <100 m , m , m , 5.48 >1000 m Distance to highways <100 m , m , m , 2.89 >1000 m IQR, interquartile range. 1 Reference cohort for hazard ratio calculation assigned a HR value of 1. recipients transplanted between 1997 and 2009, the study showed that patients living within 171 m of a major road were more than twice as likely to develop CLAD or die than those living farther away (HR 2.06; 95% CI , HR 2.20; 95% CI , respectively). In this report, we assessed the impact of TRAP on development of CLAD and mortality in a large cohort of 397 lung transplant recipients over a longer follow-up period. Our retrospective study identifies an association between the density of roadways around the home of a lung transplant recipient and an increased risk of CLAD. The risk of CLAD was also increased for transplant recipients living within 100 m of a highway. While these associations are based upon a small number of patients, they meet criteria generally used for the assessment of statistical significance. Distance from a patient s home to nearest major road was not associated with a significantly increased risk of CLAD in our cohort of patients. Our results differ from those of the Belgian research group (20) in that roadway density around a patient s home American Journal of Transplantation 2014; 14: Table 5: Hazard ratios and 95% confidence intervals (95% CI) for the associations of CLAD with every IQR increase of road density within 200 m buffer of residential addresses, by selected characteristics Covariates events Incidence of CLAD Hazard ratio 95% CI p-value for interaction Age < , > , 1.88 Sex Men , Women , 3.09 Sex-matching M M or F F , M F or F M , 2.11 Urban area Yes , 1.59 No 1 34 CLAD, chronic lung allograft dysfunction; IQR, interquartile range. 1 Cox model failed to converge due to small number of subjects. Table 6: Hazard ratio and 95% confidence interval (95% CI) for the associations between road density within 200 m buffer from major roads and highways and incident diagnosis of CLAD Model cases Hazard ratio CLAD 95% CI þage, sex , 1.40 þall other individual-level , 1.53 variables 1 þthree neighborhood-level , 1.58 education, unemployment and household income þ% Immigrant population , 1.58 þa frailty term (random effect) to investigate spatial dependence as a source of bias, using Census divisions , 1.57 Census subdivisions , 1.57 CLAD, chronic lung allograft dysfunction. 1 Individual-level covariates include treatment type, pretreatment diagnosis, donor age, donor sex, sex matching between donor and recipient. 2 Census division is the general term for provincially legislated areas (such as county and regional district) or their equivalents. Census subdivision is the general term for municipalities (as determined by provincial/territorial legislation) or areas treated as municipal equivalents for statistical purposes (e.g., Indian reserves, Indian settlements and unorganized territories). There are a total of 49 census divisions and 947 census subdivisions in Ontario, according to 1996 Canadian Census. 2753

6 Bhinder et al was a stronger predictor of CLAD than proximity to a major road, and the lack of an association between TRAP exposure estimates and mortality. Belgium has the highest roadway density in Europe and fifth highest in the world, with an overall roadway density of 504 km/100 km 2 (27). It is likely that TRAP concentrations are higher and/or TRAP contributes to a larger proportion of ambient air pollution in Belgium than in Ontario where the overall roadway density is significantly lower at 29.2 km/100 km 2 (28). Southern Ontario, home to 92% of our patients, has a roadway density only a fraction of that in Belgium, at km/ 100 km 2 (28). Domiciliary proximity to a major roadway in Ontario is likely associated with lower TRAP exposure than in Belgium. This could explain the lack of a significant association of the risk of CLAD and mortality with proximity to a major roadway in our patient population, which places the results of the Belgian cohort in the context of areas with lower traffic density. When applied across regions of greatly varying roadway density, distance from a patient s home to nearest roadway may lose its strength as a surrogate measure of TRAP exposure. A home located further from a major road in a neighborhood of high roadway density may have higher associated TRAP concentrations than a home close to a major road in a neighborhood of low roadway density. Density of roadways around a patient s home would be expected to have a stronger correlation with TRAP in regions with variable traffic density. This may explain the differences between our study and the Belgian study with respect to which surrogate measures of TRAP showed significant association with outcomes of CLAD and mortality. The composition of TRAP is also different in Canada and Belgium, given the predominance of diesel fuel as primary fuel source within Belgium and gasoline in Canada. Diesel accounts for 80% of road sector energy consumption in Belgium but only 34% in Canada (27). Further, since cars in Canada are almost exclusively gasoline fueled, the TRAP produced on the roads near most homes comes predominantly from gasoline combustion whereas most of the diesel exhaust emissions originate from trucks on major roads and highways. Studies have shown that diesel exhaust emissions have a higher oxidative potential, and in animal studies, have been associated with increased airway inflammation. Because of the ubiquitous and involuntary nature of exposure to ambient air pollution, even a modest impact of air pollution on this highly susceptible population may have an important clinical impact. Our study extends the previous Belgian findings in several important ways. Using the unique lung transplant program and databases in Ontario, we were able to assemble a larger study cohort. To better understand the impact of air pollution, we extended the previous study by carefully evaluating various exposure metrics including distance to roadway, road density, state-of-the-art satellite-based NO 2 estimates, and spatially interpolated estimates of PM 2.5 and O 3. We note that exposure to PM 2.5 has been shown to increase the risk for major chronic conditions such as diabetes and hypertension in the province of Ontario (29,30). Additionally, our study excluded single lung transplant recipients to rule out an effect of pollution on native lung function. In the Belgian study, about a quarter of the subjects were single lung transplant recipients. With respect to development of CLAD and mortality, one cannot rule out the effect of TRAP on native lung disease as a cause for a reduction. Last, we note that we are finding positive associations for what we believe are lower TRAP exposures than in many major cities in Europe, and this may argue for more focus on evaluating TRAP exposure in Canada, which would benefit not only lung transplant patients but also the general population. It should be noted that the regional pollutants that are currently measured at monitoring sites across Canada are poorly reflective of TRAP. TRAP is estimated to contribute only 10% of the PM 2.5 measured, and differs in composition and size from pollutants that are measured as part of the regional PM 2.5 concentrations. TRAP contains nontailpipe emissions from brakes and tires, and tailpipe emissions in the ultrafine particulate range (<100 nm in aerodiameter). These include trace metals and a high fraction of black and organic carbons, which have been associated with significant adverse health effects (28,31 33). Similarly O 3 is also a regional pollutant that typically is poorly reflective of TRAPs. It exhibits little spatial variability across the region studied, and may in fact have lower concentrations in regions of high traffic. While NO 2 is often used as an indicator of TRAP exposure (34,35), the satellite-based method we used to infer NO 2 exposure likely lacked adequate spatial resolution to properly capture the nearroad spatial variability of TRAP across the region. Thus while HRs greater than 1 were found for all three of these pollutants (PM 2.5,O 3 and NO 2 ), none of the associations were significant. An association between bronchoalveolar lavage cellularity and PM 10 (particulate matter pollutants 10 mm aerodiameter) has been identified in a recent prospective Belgian study using interpolated values for PM 10 (36). PM 10 contains a sizable proportion of biologic materials such as endotoxin, pollen and fungi as well as ground material and debris, in addition to the particles that comprise PM 2.5, (37) and is generally regarded as a poor measure of TRAP. Thus, it would be difficult to extrapolate these observations of the health effects of PM 10 exposure to TRAP. Recent mandates from the US Environmental Protection Agency and Health Canada to conduct near-road monitoring of NO 2 and ultrafine particles in the United States and Canada, respectively, will offer better measurements of TRAP and 2754 American Journal of Transplantation 2014; 14:

7 Pollution and Chronic Lung Allograft Dysfunction will allow better correlations of TRAP exposure on health outcomes in future studies. Multiple large-scale population studies have shown an association between exposure to ambient air pollutant and development of asthma and impaired lung development in children, as well as increased cardiorespiratory morbidity and mortality in those with existing chronic respiratory and cardiac diseases (38 44). Other than this report and those from the Belgium group, the effect of ambient air pollution on solid allograft function has not been previously studied. However, an association between increased cardiac events has been identified in renal transplant recipients. In a large, retrospective cohort study of renal transplant recipients, an increase in ambient ozone concentration was associated with a significantly increased risk of cardiac mortality (45). No association was observed between PM 10 or ozone exposure and noncardiac mortality. In a related cohort of renal transplant patients, females were specifically found to be at increased risk of cardiac mortality with increased exposure to ambient ozone (38). Variability in traffic and population density, motor vehicle fuel type and exhaust output, and constituent components of ambient air pollution warrant additional assessment as possible modifiers of the relationship between TRAP and lung transplant outcomes in other geographic patient cohorts. Our study has a few additional limitations. First, due to the large geographic area served by the Toronto Lung Transplant Program, many patients are required to reside in the Toronto area temporarily for a minimum of 3 months immediately posttransplant before returning to their permanent residences. For patients who reside in areas of lower pollution, this would mean much higher TRAP exposure in the early posttransplant period, a factor that is likely underestimated in our study as we used only permanent home address. If exposure during the early posttransplant period is critical to attainment of maximal graft function or subsequent development of CLAD, then this could have a significant bearing on our results. Our study assessed the impact of air pollution on the development of CLAD. The impact of air pollution on the development of CLAD may be associated with one CLAD phenotype versus the other (bronchiolitis obliterans vs. restrictive allograft syndrome). The size of our study cohort limited our ability to elucidate a potential association between CLAD phenotypes and TRAP exposure. Our study did not correct or control for the use of azithromycin and the development of CLAD. It has been shown that azithromycin has a protective effect on lymphocytic bronchiolitis in the posttransplant setting for lung recipients (36). Generally, our program initiates azithromycin therapy at physician discretion in response to drops in lung function. Most patients prescribed American Journal of Transplantation 2014; 14: azithromycin had already developed CLAD or subsequently met lung function criteria for CLAD. As azithromycin therapy was nearly always triggered by a drop in lung function, we did not expect to see a protective effect for azithromycin for development of CLAD and did not adjust for azithromycin in our analysis. Last, while we found associations between CLAD and nearby traffic, our study did not directly assess the air quality within patients homes. As a result, the role, if any, of factors such as the presence or absence of indoor air purifiers, quality of weather stripping and window and door sealing, presence of oil/gas or electric central or room heating could not be determined in our study. Additionally, the presence or absence of air conditioning and the resulting impact of having open versus closed windows during summer months may have had an effect on indoor air quality and may also have affected CLAD and mortality outcomes. Such measurements would support the development of exposure control measures to mitigate TRAP exposure within the home and personal environment of lung transplant recipients. These may come in the form of current home environment control methods such as window and door sealing, indoor air filtration and purification systems and central air conditioning. More generally such studies would also allow investigation of the impacts of other domestic sources such as central heating and cooking on patient exposure to air pollution. Thus future studies should directly measure pollution exposure through personal monitoring systems to clarify these questions. In conclusion, our study has demonstrated an association between higher roadway density around the home of a patient and an increased risk of development of CLAD. Additionally, we have identified an association between close proximity to a major highway and increased risk of CLAD. These observations suggest that exposure to TRAP is associated with worse outcome following lung transplantation. As well, this association is stronger for TRAP as compared to more regional air pollutants such as O 3 and PM 2.5. Additional research is under way to refine the characterization and measurement of TRAP exposure at the household and individual level in this patient population. Taken together, the findings of this research will help in refining the attributable risk of TRAP exposure, and to elucidate the mechanism by which TRAP exposure can lead to allograft dysfunction. Acknowledgments The study used data from Trillium Gift of Life, Toronto General Hospital Multi- Organ Transplant Program, Public Health Ontario, Southern Ontario Centre for Atmospheric Aerosol Research and was funded by the Canadian Foundation for Innovation and the Ontario Ministry for Research and Innovation. We are grateful to Colin Lee for providing the satellite remote sensing-based exposure estimates and Steven Johnson at Public Health Ontario for providing GIS support. The NAPS fixed-site data were provided by Environment Canada and the Ontario Ministry of the Environment. 2755

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