Article Figures & Tables
Figures
- Figure 1:
Flow chart for cohort.
- Figure 2:
Probability of developing asthma by region of birth, censored at age 10 years.
Tables
Characteristic LHIN subregion; no. (%) of patients* p value Lambton
n = 16 758Windsor
n = 34 962London–Middlesex
n = 62 707Maternal characteristics at delivery date Age, yr, mean ± SD 27.94 ± 5.37 28.30 ± 5.47 29.11 ± 5.44 < 0.001 Age group, yr 15–29 10 203 (60.9) 20 261 (58.0) 31 930 (50.9) < 0.001 30–39 6285 (37.5) 14 029 (40.1) 29 366 (46.8) 40–49 270 (1.6) 672 (1.9) 1411 (2.3) Rural geography 4557 (27.2) 15 (0.0) 3264 (5.2) < 0.001 Income quintile 1 (lowest) 3918 (23.4) 10 971 (31.4) 14 272 (22.8) < 0.001 2 3408 (20.3) 9105 (26.0) 13 397 (21.4) 3 3394 (20.3) 7551 (21.6) 12 723 (20.3) 4 3406 (20.3) 4083 (11.7) 12 277 (19.6) 5 (highest) 2509 (15.0) 3200 (9.2) 9887 (15.8) Missing 123 (0.7) 52 (0.1) 151 (0.2) Residential instability 1 (least instability) 2391 (14.3) 2810 (8.0) 9436 (15.0) < 0.001 2 3483 (20.8) 4783 (13.7) 11 554 (18.4) 3 4533 (27.0) 6985 (20.0) 11 834 (18.9) 4 3681 (22.0) 11 184 (32.0) 13 382 (21.3) 5 (most instability) 2670 (15.9) 9200 (26.3) 16 501 (26.3) Material deprivation 1 (least deprived) 2541 (15.2) 3993 (11.4) 11 889 (19.0) < 0.001 2 3319 (19.8) 6411 (18.3) 10 960 (17.5) 3 3400 (20.3) 5455 (15.6) 13 039 (20.8) 4 3114 (18.6) 6975 (20.0) 13 119 (20.9) 5 (most deprived) 4384 (26.2) 12 128 (34.7) 13 700 (21.8) Dependency 1 (lowest 1543 (9.2) 5591 (16.0) 15 393 (24.5) < 0.001 2 2934 (17.5) 7869 (22.5) 16 275 (26.0) 3 3575 (21.3) 7872 (22.5) 14 897 (23.8) 4 4277 (25.5) 8810 (25.2) 9438 (15.1) 5 (highest 4429 (26.4) 4820 (13.8) 6704 (10.7) Ethnic concentration 1 (lowest) 6903 (41.2) 3509 (10.0) 9437 (15.0) < 0.001 2 4688 (28.0) 4400 (12.6) 11 755 (18.7) 3 3435 (20.5) 6268 (17.9) 17 248 (27.5) 4 1553 (9.3) 10 080 (28.8) 15 731 (25.1) 5 (highest) 179 (1.1) 10 705 (30.6) 8536 (13.6) Newborn characteristics Sex, female 8224 (49.1) 16 982 (48.6) 30 543 (48.7) 0.6 Low birth weight or preterm† 1445 (8.6) 3104 (8.9) 5533 (8.8) 0.6 Pollutant exposures in year of birth NO2,‡ ppb, mean ± SD 28.4 ± 4.8 34.9 ± 3.9 28.5 ± 4.2 < 0.001 O3,‡ ppb, mean ± SD 41.8 ± 1.9 39.6 ± 2.6 40.3 ± 2.0 < 0.001 PM2.5,‡ ppb, mean ± SD 23.6 ± 2.8 21.3 ± 1.5 17.7 ± 1.6 < 0.001 SO2,‡ ppb, mean ± SD 8.8 ± 1.8 6.6 ± 1.7 2.75 ± 0.9 < 0.001 Note: LHIN = Local Health Integration Network, NO2 = nitrogen dioxide, O3 = ozone, PM2.5 = fine particulate matter, ppb = parts per billion, SD = standard deviation, SO2 = sulphur dioxide.
↵* Except where indicated otherwise.
↵† Low birth weight or preterm refers to infants born with low birth weight < 2500 g, small for gestational age, intrauterine growth restriction or preterm gestation < 37 weeks. All diagnostic codes are detailed in Appendix 1, Table S1.
↵‡ NO2 and O3 data were available for the period Jan. 1, 1996, to Mar. 31, 2009; PM2.5 data for the period Jan. 1, 2003, to Mar. 31, 2009; and SO2 data for the period Apr. 1, 1993, to Mar. 31, 2009 (full study period). Pollution values were based on annual summaries and were assigned to children at the time (i.e., year) of birth and location of birth (i.e., residential Forward Sortation Area [geographic unit based on postal code with 400–700 persons living there] or city region of birth, depending on the source of the data).
- Table 2:
Cox proportional hazards estimates for the development of asthma by age 10 years, stratified by era
Birth (fiscal) year and LHIN subregion HR (95% CI) Unadjusted Adjusted* Adjusted† 1993–1996 Lambton 1.00 (Ref.) 1.00 (Ref.) NA Windsor 0.68 (0.64–0.73) 0.60 (0.56–0.65) London–Middlesex 0.57 (0.54–0.61) 0.54 (0.51–0.58) 1997–2000 Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.84 (0.77–0.90) 0.77 (0.71–0.84) NA London–Middlesex 0.63 (0.59–0.68) 0.61 (0.56–0.66) 2001–2004 Lambton 1.00 (Ref.) 1.00 (Ref.) 1.00 (Ref.) Windsor 0.90 (0.83–0.97) 0.80 (0.73–0.88) 0.81 (0.72–0.91) London–Middlesex 0.69 (0.64–0.75) 0.65 (0.60–0.71) 0.65 (0.58–0.72) (Jan. 1, 2003–Mar 31, 2005; n = 15 558) 2005–2008 Lambton 1.00 (Ref.) 1.00 (Ref.) 1.00 (Ref.) Windsor 0.85 (0.78–0.92) 0.67 (0.61–0.74) 0.67 (0.61–0.74) London–Middlesex 0.77 (0.71–0.83) 0.65 (0.60–0.71) 0.65 (0.60–0.71) (n = 29 179) 1993–2008 (all years) Lambton 1.00 (Ref.) 1.00 (Ref.) 1.00 (Ref.) Windsor 0.81 (0.78–0.84) 0.70 (0.67–0.73) 0.72 (0.67–0.77) London–Middlesex 0.66 (0.63–0.68) 0.61 (0.58–0.63) (n = 114 427) 0.65 (0.61–0.69) (n = 44 737) Note: CI = confidence interval, HR = hazard ratio, LHIN = Local Health Integration Network, NA = not available, Ref. = reference category.
↵* Adjusted for maternal age, maternal asthma, sex, rural geography, neighbourhood material deprivation, neighbourhood ethnic concentration, cesarean delivery and fiscal year. The number of individuals per model is variable because the cohorts were restricted to children with no missing data for exposures to pollutants.
↵† Adjusted for all variables listed above and restricted to children with data available for exposures to all pollutants.
- Table 3:
Association of individual air pollution exposures with adjusted Cox proportional hazards estimates for development of asthma by age 10 years
Model and LHIN subregion Hazard ratio (95% CI) Adjusted* Adjusted† (Jan. 1, 2003–Mar. 31, 2009)
n = 44 737Model with no pollutants Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.7 (0.67–0.73) 0.72 (0.67–0.77) London–Middlesex 0.61 (0.58–0.63)
(Apr. 1, 1993–Mar. 31, 2009; n = 114 427)0.65 (0.61–0.69) Model A: NO2 Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.72 (0.67–0.77) 0.70 (0.62–0.81) London–Middlesex 0.63 (0.60–0.66)
(Jan 1, 1996–Mar 31, 2009; n = 92 809)0.65 (0.60–0.69) Model B: O3 Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.73 (0.69–0.77) 0.72 (0.67–0.78) London–Middlesex 0.62 (0.59–0.65)
(Jan. 1, 1996–Mar. 31, 2009; n = 92 809)0.65 (0.60–0.69) Model C: SO2 Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.72 (0.68–0.75) 0.80 (0.68–0.93) London–Middlesex 0.64 (0.59–0.69)
(Apr. 1, 1993–Mar. 31, 2009; n = 114 427)0.81 (0.60–1.09) Model D: PM2.5 Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.75 (0.69–0.82) 0.75 (0.69–0.82) London–Middlesex 0.71 (0.63–0.81)
(Jan 1, 2003–Mar 31, 2009; n = 44 737)0.71 (0.63–0.81) Model E: all pollutants combined Lambton 1.00 (Ref.) 1.00 (Ref.) Windsor 0.79 (0.62–1.01) 0.79 (0.62–1.01) London–Middlesex 0.89 (0.64–1.24)
(Jan. 1, 2003–Mar. 31, 2009; n = 44 737)0.89 (0.64–1.24) Note: CI = confidence interval, LHIN = Local Health Integration Network, NO2 = nitrogen dioxide, O3 = ground-level ozone, PM2.5 = particulate matter 2.5 um or smaller, Ref. = reference category, SO2 = sulphur dioxide.
↵* Adjusted for maternal age, maternal asthma, sex, rural geography, neighbourhood material deprivation, neighbourhood ethnic concentration, cesarean delivery and fiscal year. The number of individuals per model is variable because the cohorts were restricted to children with no missing data for exposures to pollutants.
↵† Adjusted for all variables listed above, with sample size of cohorts restricted to children with available information on exposures to all pollutants.
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