Covariate patterns were formed that con- trolled for age, sex, race/ethnicity, MHI, and exposure. The outcome for each covariate pat- tern was the number of hospital discharge diagnoses across all the ZIP codes having that covariate pattern. We used separate negative binomial, log-linear regression models to esti- mate associations between exposure [modeled as categorical indicator variables for fuel-only, waste-only, or fuel-and-waste vs. clean ZIP codes (referent)], and hospitalization rates among those < 10 or ≥ 10 years of age, with adjustment for potential confounders. For children < 10 years of age, we estimated asso- ciations between exposure and hospitaliza- tion rates for asthma or ARI using separate models adjusted for sex, race/ethnicity (black or white), age (categorical: 1–2, 3–5, or 6–9 vs. 0 years), MHI (categorical: first-, second-, or third-quartile MHI vs. fourth-quartile MHI), and urban/rural ZIP code. For those ≥ 10 years of age, we estimated associations with hospitalization for asthma, ARI, or COPD using separate models adjusted for the same covariates but with age categorized as 25–49, 50–74, or ≥ 75 versus 10–24 years. All statistical analyses were performed with SAS software (version 9.2; SAS Institute Inc., Cary, NC, USA). p-Value < 0.05 was selected as the critical value for statistical sig- nificance for all statistical tests. The PROC GENMOD procedure was used for nega- tive binomial regression analysis (Huang et al. 2006; Shcherbatykh et al. 2005). Results During 1993–2008, there were 90,773 asthma and 98,298 ARI hospitalizations for children < 10 years of age, and 820,671 asthma, 233,171 ARI, and 1,948,903 COPD hospitalizations among those ≥ 10 years of age, in the 1,252 ZIP codes included in the analy- sis (Table 1). Although African Americans contributed only 8.7% of the person- years studied, they accounted for 17.8% of asthma and 13.7% of ARI hospitalizations. Crude hospitalization rates in both fuel- only and waste-only ZIP codes were signifi- cantly higher than those in clean ZIP codes for all outcomes with the exception of rates of asthma and ARI in fuel-only ZIP codes among those < 10 years of age (Table 2). Crude discharge rates for all outcomes were higher in ZIP codes with a fuel-fired power plant and a hazardous waste site than in ZIP codes with only a fuel or waste site. In gen- eral, these associations were maintained when estimates were stratified according to age (< 10 or ≥ 10 years) and sex and race/ethnicity [see Supplemental Material, Table S3 (http:// dx.doi.org/10.1289/ehp.1104146)]. After adjusting for known confounders (sex, race/ethnicity, age, MHI, urban/rural), living in a fuel-only ZIP code was associated with slightly elevated (not significant) rates of asthma and ARI hospitalization compared with living in a clean ZIP code (Table 3). Residence in a waste-only ZIP code, however, was associated with significantly increased RRs for hospitalization for asthma (RR = 1.11; 95% CI: 1.03, 1.19) and ARI (RR = 1.13; 95% CI 1.05, 1.21) relative to clean ZIP codes. Stronger associations were observed with residence in a fuel-and-waste ZIP code (respectively, RR = 1.19; 95% CI: 1.11, 1.28; and RR = 1.24; 95% CI: 1.15, 1.33). Among those ≥ 10 years of age, RRs were significantly elevated among residents in Hospital discharge rate per 100,000 (95% CI) Table 2. Crude hospital discharge rates for asthma, ARI, and COPD according to age and exposure after excluding extremes of MHI status. Person-years 8,661,904 567,857 8,939,610 3,355,019 56,609,900 3,962,094 60,539,925 21,653,627 Asthma 359 (355, 363) 381 (365, 397) 452 (448, 457) 509 (501, 517) 512 (510, 513) 570 (563, 578) 599 (597, 601) 672 (669, 676) ARI 404 (400, 409) 414 (397, 431) 474 (470, 479) 551 (544, 559) 147 (146, 148) 154 (151, 158) 169 (168, 170) 192 (191, 194) COPD 1,222 (1,219, 1,225) 1,390 (1,379, 1,402) 1,401 (1,398, 1,404) 1,627 (1,622, 1,633) Exposure Age < 10 years Clean Fuel only Waste only Fuel and waste Age ≥ 10 years Clean Fuel only Waste only Fuel and waste Exposure Clean Fuel only Waste only Fuel and waste Environmental Health Perspectives • volume 120 | number 6 | June 2012 Table 3. Adjusted RRs of hospital discharge for asthma, ARI, and COPD as a function of residence in ZIP codes with different exposure status. Asthma Age < 10 years RR (95% CI) 1.00 1.01 (0.91, 1.12) 1.11 (1.03, 1.19) 1.19 (1.11, 1.28) p-Value 0.85 0.005 < 0.0001 Age ≥ 10 years RR (95% CI) p-Value 1.00 1.11 (1.02, 1.20) 0.01 1.07 (1.00, 1.14) 0.04 1.18 (1.11, 1.26) < 0.0001 ARI Age < 10 years RR (95% CI) 1.00 1.03 (0.93, 1.14) 1.13 (1.05, 1.21) 1.24 (1.15, 1.33) p-Value 0.56 0.001 < 0.0001 Age ≥ 10 years RR (95% CI) p-Value 1.00 1.15 (1.05, 1.27) 0.003 1.09 (1.02, 1.17) 0.01 1.21 (1.13, 1.30) < 0.0001 COPD Age ≥ 10 years RR (95% CI) 1.00 1.17 (1.06, 1.29) 1.16 (1.08, 1.26) 1.26 (1.17, 1.37) Power plants and respiratory diseases fuel-only ZIP codes compared with clean ZIP codes for asthma (RR = 1.11; 95% CI: 1.02, 1.20), ARI (RR = 1.15; 95% CI: 1.05, 1.27), and COPD (RR = 1.17; 95% CI: 1.06, 1.29) and slightly higher than corresponding RRs for waste-only ZIP codes (Table 3). The larg- est RRs estimated for all outcomes were for fuel-and-waste ZIP codes. The RRs for resi- dence in a ZIP code with both exposures were consistent with expectations assuming additive effects of residence in fuel-only and waste-only ZIP codes. Supplemental Material, Table S4 (http://dx.doi.org/10.1289/ehp.1104146), shows the relation of hospital discharge for asthma, ARI, and COPD with covariates, sex, race/ethnicity, age, income, and urban/rural residence for those < 10 and ≥ 10 years of age. Hospitalization rates in all interaction sub- groups with sex, race/ethnicity, age, MHI, and urban/rural status were compared to identify effect modifiers (data not shown). There was no statistically significant effect on the RR or improvement in the overall quality of fit (deviance/degree of freedom) upon consider- ation of most interaction subgroups, and we did not see any evidence of significant interac- tions (p > 0.05 based on deviance statistics). Discussion There is mounting evidence that environ- mental exposures increase the risk of human disease, and these exposures come from mul- tiple sources, including air pollutants coming from fossil-fuel combustion and hazardous chemicals found in waste sites and many other places. Although many of the important sources of air pollutants are mobile, power plants, because they are stationary, constitute a localized source of air toxics and thus allow one to examine whether individuals living near these power plants experience greater exposure and more disease as a result. The goal of this study was to examine rates of hospitalization for asthma and respiratory infection among individuals who live near fuel power plants. Because previous studies from our group have reported elevated rates of hospitalization for these same diseases among individuals living near hazardous waste sites (Carpenter et al. 2008; Ma et al. 2007), we have reexamined these relationships now with more years of data to assess the rate of hospitalization among individuals who live near both a fuel-fired power plant and a hazardous waste site. p-Value 0.002 0.0001 < 0.0001 809