Wong et al. statistically significant (p < 0.05) for CVD baseline level of influenza (ER, 1.1% and 0.46% for ARD in all‑ages and 0.40% for associated with NO2 and SO2, and for RD 1.5% for all‑ages and ≥ 65 age groups). We COPD in ≥ 65 age group when influenza associated with NO2 (ER, 1.23%, 1.64%, found modifying effects of influenza for the intensity increased from 0 to 10% (Table 4). and 1.24%, respectively) but were not sig‑ effect of SO2 on hospitalization to be sig‑ In analyses stratified by males and females, nificant (p > 0.05) for all mortality outcomes nificant (p ≤ 0.05) only for ARD in all‑ ages we found significant effect modification of associated with O3 (Table 2). We found sig‑ group with ER increased 0.86% (Table 3). influenza (p ≤ 0.05) for the effects of O3 nificant modifying effects of influenza for the For PM10, we found significant effects on hospitalization, with increases of 0.38% O3 effects on mortality for RD and COPD (p ≤ 0.05) at the baseline level of influenza and 0.48% in ER for RD in both males and (ER increased 0.59% and 1.05%) but not for for all the health outcomes under study (ER females in the ≥ 65 age groups, respectively; the other pollutants. ranging from 0.55% to 1.49%). We found and with increase of 0.63% and 0.88% in The effects of NO2 on hospitalization at no significant modifying effects of influenza ER for COPD in the females of all‑ages and the baseline level of influenza were statistically for PM10 on hospitalization in all the disease ≥ 65 groups, respectively. The effect modifica‑ significant (p ≤ 0.05) for all the health out‑ categories under study (Table 4). tions of influenza on hospitalization associated comes under study (except for ARD), with ER We found significant effects of O3 at the with O3 tend to be higher and more signif‑ ranging from 0.85% to 1.84%. We found sig‑ baseline level of influenza (p ≤ 0.01) for all RD icant for females than for males (Table 5). nificant (p ≤ 0.05) modifying effects of influ‑ groups under study (ER ranged from 0.53% We found no significant effect modification enza for the NO2 effects on hospitalization of to 1.39%), but not for CVD disease. Changes of influenza for effects of the other pollut‑ COPD in the groups ≥ 65 years of age (ER in ER associated with O3 for hospitalization of ants on hospitalization in most health out‑ increased 0.43%; Table 3). RD were significant (p ≤ 0.05). ER increased comes under study, except for NO2 with an We found significant (p ≤ 0.001) effects 0.24% and 0.40% for RD in all‑ages and increased ER on COPD in the males in the of SO2 on hospitalization of CVD at the ≥ 65 age groups, respectively, and increased ≥ 65 group, and for PM10 with decreased ER on RD in the males in the alla‑ges group Table 2. Modifying effects of influenza for the four pollutant effects on mortality. [data not shown; see Supplemental Material, Effect at mean Tables 1–3 (http://www.ehponline.org/ Modifying effecta Baseline effectb level of influenza intensityc members/2008/11605/suppl.pdf)]. Pollutant Disease ER 95% CI p-Value ER 95% CI p-Value ER 95% CI p-Value Discussion NO2 RD 0.18 –0.45 to 0.82 NS 1.24 0.27 to 2.22 * 1.42 0.45 to 2.41 ** COPD 1.01 –0.03 to 2.05 NS 0.26 –1.34 to 1.87 NS 1.26 –0.33 to 2.89 NS Previous studies have identified modifying CVD 0.15 –0.39 to 0.70 NS 1.23 0.41 to 2.06 ** 1.39 0.56 to 2.22 # effects of climates for the short‑ term effects SO2 RD 0.05 –1.12 to 1.23 NS 1.20 –0.38 to 2.81 NS 1.25 –0.35 to 2.88 NS of air pollutants on mortality; for example, COPD 0.32 –1.58 to 2.27 NS –0.03 –2.67 to 2.69 NS 0.30 –2.35 to 3.01 NS the effects of air pollutants were higher in the CVD –0.45 –1.45 to 0.55 NS 1.64 0.27 to 3.02 * 1.18 –0.20 to 2.57 NS warm season (Katsouyanni et al. 1997), but PM10 RD 0.08 –0.39 to 0.55 NS 0.69 –0.10 to 1.49 NS 0.77 –0.01 to 1.56 NS other reports found no noticeable changes COPD 0.50 –0.26 to 1.27 NS –0.05 –1.36 to 1.28 NS 0.45 –0.83 to 1.75 NS CVD 0.25 –0.15 to 0.65 NS 0.45 –0.23 to 1.13 NS 0.70 0.03 to 1.37 * between seasons (Schwartz 2000) or even found larger effects in the cool season (Wong O RD 0.59 0.04 to 1.14 * –0.16 –1.00 to 0.69 NS 0.42 –0.44 to 1.29 NS 3 COPD 1.05 0.17 to 1.93 * –0.11 –1.51 to 1.32 NS 0.94 –0.49 to 2.38 NS et al. 2002). Other effect modifiers have been CVD 0.04 –0.42 to 0.51 NS 0.58 –0.15 to 1.31 NS 0.62 –0.12 to 1.36 NS identified as well, such as NO2 concentration, which markedly modified the effects of PM10 Abbreviations: CI, confidence interval; NS, not significant. aChange in ER per 10-µg/m3 increase in concentration of air pollutant averaged over the lag 0 and lag 1 days when on mortality (Katsouyanni et al. 2001). Our influenza intensity changed from the baseline (0%) to the mean level (10%). bER per 10-µg/m3 increase in concentration study demonstrated effect modification by of air pollutant averaged over the lag 0 and lag 1 days when influenza intensity is assumed equal to 0. cER per 10-µg/m3 influenza on the effects of single air pollut‑ increase in concentration of air pollutant averaged over the lag 0 and lag 1 days when intensity is assumed equal to 10% (mean level of influenza intensity). *0.01 < p ≤ 0.05; **0.001 < p ≤ 0.01; #p ≤ 0.001. ants, particularly O3, both on mortality and Table 3. Modifying effects of influenza for NO2 and SO2 effects on hospitalization. Modifying effecta Baseline effectb Effect at mean level of influenza intensityc Pollutant Disease Age group (years) ER 95% CI p-Value ER 95% CI p-Value ER 95% CI p-Value NO2 RD All –0.09 –0.32 to 0.15 NS 0.85 0.51 to 1.18 # 0.76 0.51 to 1.01 # ≥ 65 –0.07 –0.35 to 0.22 NS 1.06 0.64 to 1.48 # 0.99 0.68 to 1.30 # ARD All 0.33 –0.03 to 0.70 NS 0.55 –0.02 to 1.12 NS 0.88 0.46 to 1.31 # 0–14 –0.18 –0.57 to 0.22 NS 0.44 –0.16 to 1.04 NS 0.26 –0.19 to 0.71 NS COPD All 0.09 –0.26 to 0.44 NS 1.84 1.32 to 2.35 # 1.93 1.54 to 2.32 # ≥ 65 0.43 0.05 to 0.81 * 1.19 0.62 to 1.76 # 1.62 1.19 to 2.06 # CVD All 0.04 –0.20 to 0.28 NS 0.98 0.63 to 1.33 # 1.02 0.76 to 1.29 # ≥ 65 –0.03 –0.32 to 0.26 NS 1.30 0.89 to 1.70 # 1.27 0.96 to 1.57 # SO2 RD All –0.24 –0.65 to 0.16 NS 0.31 –0.23 to 0.86 NS 0.07 –0.30 to 0.44 NS ≥ 65 –0.33 –0.83 to 0.17 NS 0.37 –0.30 to 1.05 NS 0.04 –0.42 to 0.50 NS ARD All 0.86 0.20 to 1.53 * –0.77 –1.69 to 0.16 NS 0.09 –0.55 to 0.73 NS 0–14 0.53 –0.16 to 1.22 NS –0.60 –1.56 to 0.37 NS –0.07 –0.74 to 0.60 NS COPD All 0.35 –0.32 to 1.02 NS 0.29 –0.57 to 1.16 NS 0.64 0.04 to 1.25 * ≥ 65 0.41 –0.29 to 1.13 NS 0.17 –0.77 to 1.12 NS 0.58 –0.07 to 1.24 NS CVD All –0.15 –0.60 to 0.30 NS 1.10 0.52 to 1.69 # 0.95 0.54 to 1.36 # ≥ 65 –0.28 –0.80 to 0.25 NS 1.50 0.83 to 2.17 # 1.22 0.75 to 1.69 # Abbreviations: CI, confidence interval; NS, not significant. aChange in ER per 10-µg/m3 increase in concentration of air pollutant averaged over the lag 0 and lag 1 days when influenza intensity changed from the baseline (0%) to the mean level (10%). bER per 10-µg/m3 increase in concentration of air pollutant averaged over the lag 0 and lag 1 days when influenza intensity is assumed equal to 0. cER per 10-µg/m3 increase in concentration of air pollutant averaged over the lag 0 and lag 1 days when intensity is assumed equal to 10% (mean level of influenza intensity). *0.01 < p ≤ 0.05; #p ≤ 0.001. 250 117 | number 2 | February 2009 • Environmental Health Perspectives ovlume