TABLE 1.
Characteristics and results of included studies with health services use outcomes
| Reference; study location; and study period | Study design; study population and size | Pollutants (mean or median levels*) and methods assessing exposure | Respiratory outcome | Study findings | Adjustment for confounding factors |
|---|---|---|---|---|---|
| Lin et al, 2004 (34); Vancouver area; 1987–1998 | Time series study; hospitalizations of 6–12 year olds; from BC Linked Health Dataset (n=3822) | Mean CO (960), SO2 (4.77), NO2 (18.65), O3 (28.02), PM10 (NS), PM2.5 (NS) from 1995–1998; from monitoring stations | Hospitalizations for asthma | RR of asthma hospitalizations in low SES group associated with: NO2 (male, 1-day lag): 1.16 (95% CI 1.06–1.28), NO2 (male 4-day lag): 1.18 (95% CI 1.03–1.34), SO2 (female 4-day lag): 1.17 (95% CI 1–1.37), and SO2 (female 6-day lag): 1.19 (95% CI 1–1.42) | Sex, temperature, relative humidity, SES, day of the week |
| Yang et al, 2004 (46); Greater Vancouver; 1995–1999 | Case-crossover, case-control and time-series analyses; first hospital admissions of 0–3 year olds, excluding birth-related admissions (n=1610) | Mean CO (700), O3 (14.3), NO2 (16.8), SO2 (3.5), PM10 (13.3) and PM2.5 (7.7); from local monitors | Hospitalizations for respiratory disease (including asthma) | OR of respiratory hospitalizations associated with 3-day lag mean and max PM10-2.5: 1.22 (95% CI 1.02–1.48) and 1.14 (95% CI 0.99–1.32), respectively; time-series analysis gave weaker associations | Sex, SES, day of the week, season, study year, season and influenza hospitalizations |
| Lin et al, 2005 (35); Toronto; 1998–2001 | Case-crossover design; hospitalizations of 0–14 year olds (n=6782) | Mean PM10 (20.41), PM2.5 (9.59), PM10-2.5 (10.86), CO (1160), SO2 (4.73), NO2 (24.54), O3 (38.06); from monitoring stations | Hospitalization for respiratory infections | OR of hospitalizations for 6-day average exposure to: PM10-2.5: boys 1.15 (95% CI 1.02–1.3), girls 1.18 (95% CI 1.01–1.36); PM10: boys 1.25 (95% CI 1.01–1.54); NO2: girls 1.31 (95% CI 1.05–1.63); PM2.5, O3 and SO2 showed no associations | Sex, temperature, pollutant interactions and seasonality |
| Luginaah et al, 2005 (37); Windsor; 1995–2000 | Time series and case-crossover design; hospitalizations 0–14 year olds (n=1602) | Mean NO2 (38.9), SO2 (27.5), CO (1300), PM10 (50.6), TRS (8), and coefficient of haze (0.5); from monitoring stations | Hospitalizations for respiratory disease | Time Series RR: NO2: female 2-day lag: 1.19 (95% CI 1.002–1.411); SO2: female Current-Day: 1.11 (95% CI 1.011–1.221); CO: female 2-day lag: 1.07 (95% CI 1.001–1.139); Cross-over design OR: CO: female current day, 2-day lag and 3-day lag: 1.15 (95% CI 1.006–1.307), 1.19 (95% CI 1.020–1.379) and 1.22 (95% CI 1.022–1.459) | Temperature, sex, humidity, barometric pressure, seasonality |
| Dales et al, 2006 (25); 11 of the largest Canadian cities; 1986–2000 | Time series study; hospitalizations of 0–27 day olds (n=8586) | Mean NO2 (21.8), SO2 (4.3), CO (1.0), O3 (17.0), and PM10 (NS); from monitoring stations (population weighted average) | Hospitalizations for respiratory disease | The percentage of variation for IQR increase for all gasses combined was 9.61% (95% CI 4.52–14.7); individually: O3: 2.67 (95% CI 0.98–4.39); NO2 2.48 (95% CI 1.18–3.8); SO2: 1.41 (95% CI 0.35–2.47); CO: 1.3 (95% CI 0.13–2.49) | Long-term temporal trends, day of week effects, weather variables, other gases and PM10 |
| Villeneuve et al, 2007 (45); Edmonton; 1992–2002 | Case-crossover design (time stratified); ED visits of 2–14 year olds (n=20,392) | Summer/winter median PM10 (22.0/19.0), PM2.5 (7.0/7.3), CO (600/900), SO2 (2.0/3.0), NO2 (17.5/28.5), O3 (38.0/24.3); from monitoring stations | ED visits for asthma | Positive association were observed in warm season and higher in 2–4 years: OR 5-day average: NO2 1.50 (95% CI 1.31–1.71), CO 1.48 (95% CI 1.27–1.72), PM2.5: 1.16 (95% CI 1.04–1.28) and PM10: 1.16 (95% CI 1.05–1.28); For 5–14 years: OR 5-day average: NO2: 1.13 (95% CI 1.02–1.24), O3: 1.14 (95% CI 1.05–1.24), PM2.5: 1.10 (95% CI 1.02–1.17), PM10: 1.14 (95% CI 1.06–1.22); many of the 1- and 3-day lags were also significant during the warm season for various pollutants | Temperature, relative humidity, season, aeroallergens, and ED visits for influenza |
| Szyszkowicz et al, 2008 (43); Edmonton; 1992–2002 | Longitudinal study; 0–10 years ED visits (n=18,891) | Mean/median CO (700/600), NO2 (21.9/19.7), SO2 (2.6/2.2), O3 (18.6/17.8), PM10 (22.6/19.4), PM2.5 (8.5/6.2); from monitoring stations | ED visits for asthma | Many positive associations were observed in the warm season; the higher percentage increase for each pollutant was: CO (2-day lag) male: 17.7% (95% CI 10.2–25.6), NO2 (2-day lag) male: 19.2% (95% CI 11.4–27.6), O3 (same day) female: 17.8% (95% CI 7.1–29.5), PM10 (2-day lag) male: 7.4% (95% CI 3.1–11.9), PM2.5 (same-day) female: 7.7% (95% CI 5.2–10.3), O3 (1-day lag), PM10 (same-day), and PM2.5 (2-day lag) showed positive variations for some age/sex/season combinations | Sex, temperature, relative humidity, day of the week |
| Burra et al, 2009 (20); Toronto; 1992–2001 | Longitudinal study; family physician and specialists service claim records for 1–17 year olds (n=1,146,215) | Mean SO2 (9.7), NO2 (39.2), O3 (33.3) and PM2.5 (17.9); from monitoring stations | Asthma physician visits | RR for pollutants by SES quintiles (Q1/Q5) were: SO2: 1.005 (95% CI 1.000–1.010), NO2: 1.002 (95% CI 0.995–1.008), and PM2.5: 1.006 (95% CI 0.997–1.015); low SES groups had higher RR in SO2 and PM2.5 models | SES, temperature, barometric pressure, 24 h mean relative humidity, day of the week |
| Smargiassi et al, 2009 (41); Montreal (Quebec); 1996–2004 | Case-crossover design (time stratified); 2–4 year olds living near a refinery (n=1579) | Daily peak mean SO2 (east/southwest of refineries) using monitoring stations (23.8/12.8); and AERMOD dispersion model (19.2/16.0) | Asthma ED visits or hospital admissions | OR for same-day ED visits: 1.10 (95% CI 1.00–1.22), and hospital admissions: 1.42 (95% CI 1.10–1.82) | Temperature, relative humidity, regional/background air pollutant levels |
| Henderson et al, 2011 (30); Southeast corner of BC 92 days: July to September 2003 | Cohort study; Residents at the southeast area of BC with a reliable geocodable residential address in health databases; included newborns (n=281,711; 21.6% <20 years old) | Mean PM10 during days of smoke coverage from forest fires; Comparison of two methods: TEOM monitoring stations (45.9); and CALPUFF dispersion model (44.2) | Respiratory or cardiovascular physician visits and hospital admissions | OR change due to 10 μg/m3 increase in total PM10 (TEOM) in respiratory hospital admissions: 1.05 (95% CI 1.00–1.10), and cardiovascular admissions: 1.00 (95% CI 0.96–1.05) | Age, sex, SES |
| Lavigne et al, 2012 (32); Windsor (Ontario); 2002–2009 | Case-crossover design (time stratified); 2–14 year olds hospitalized for asthma (n=3728) | Mean summer/winter SO (2.1/1.7), NO2 (9.8/7.4), CO (400/300), PM2.5 (7.1/7.4), O3 (13.2/26.0); from monitoring stations | Asthma ED visits | Increased risk of warm season asthma ED visit of 19%, 25% and 36% associated with increases in IQR of 1-day lagged exposure to SO2, NO2 and CO levels, respectively | Daily number of influenza ED visits, temperature and relative humidity. |
| Lewin et al, 2013 (33); Shawiningan (Quebec); 1999–2008 | Case-crossover design (time stratified); hospitalized 0–4 year olds living near aluminium smelter (n=396) | Exposure calculated by: % of hours/day each residence was downwind of the smelter; and daily mean SO2 (6.3) and PM2.5 (13.5) from monitoring station | Hospitalization for asthma or bronchiolitis | OR of hours downwind of a smelter on same-day hospitalization of 2–4-year-old children: 1.27 (95% CI 1.03–1.56), and PM2.5 exposure: 1.22 (95% CI 1.03–1.11) | Average daily wind direction and speed |
| To et al, 2013 (44); Ontario; 2003–2006 | Longitudinal study; All Ontario residents with asthma registered at the (OASIS) database | Canada 2003/2004/2005/2006) mean AQHI (3.87/3.64/3.83/3.34), NO2 (NS), O3 (NS), and PM2.5 (NS) measures; from monitoring stations | Asthma-attributed hospitalizations, ED and outpatient visits | RR for 1-unit increase in the AQHI by same-day outpatient visits: 1.056 (95% CI 1.053–1.058) and hospitalization: 1.0256 (95% CI 1.053–1.058), and 2-day lag ED visits: 1.013 (95% CI 1.010–1.017) | Age group, season, residence area, and year |
| Szyszkowicz et al, 2014 (42); Windsor (Ontario); 2004–2010 | Case-crossover design (time stratified); ED visits for 2–14 year olds; (n=2151) | AQHI for Canada; hourly AQHI calculations, NO2, O3, and PM2.5 measures from two monitoring stations | Asthma ED visits | Positive and statistically significant associations were observed for same-day and 9-day lag exposure (both OR 1.11 [95% CI 1.01–1.21]) and 3-day lag exposure (OR 1.09 [95% CI 1.00–1.18]) | Ambient temperature, relative humidity and daily counts of ED visits for influenza |
*
Parts per billion for gasses, μg/m3 for particulate matter (PM). AQHI Air Quality Health Index; BC British Columbia; CO Carbon monoxide; ED Emergency department; IQR Interquartile range; NO2 Nitrogen dioxide; NS Not stated; O3 Ozone; OASIS Ontario Asthma Surveillance Information System; RR Relative risk; SES Socioeconomic status; SO2 Sulphur dioxide; TEOM Tapered element oscillating microbalance; TRS Total reduced sulphur