Short-term effects of air pollution on total and cardiovascular mortality - The confounding effect of influenza epidemics
ABSTRACT Air pollution is associated with total mortality. This association may be confounded by uncontrolled time-varying risk factors such as influenza epidemics.
We analyzed independent data on influenza epidemics from 7 European cities that also had data on mortality associated with particulates (PM10). We used 10 methods to control for epidemics (5 derived from influenza data and 5 from respiratory mortality series) and compared those results with analyses that did not control for these epidemics.
Adjustment for influenza epidemics increased the PM10 effect estimate in most cases (% change in the pooled regression coefficient: -1.9 to 38.9 for total mortality and 1.3 to 25.5 for cardiovascular mortality). A 10-microg/m increase in PM10 concentrations (lag 0-1) was associated with a 0.48% (95% confidence interval=0.27-0.70%) increase in daily mortality unadjusted for influenza epidemics, whereas under the various methods to control for epidemics the increase ranged from 0.45% (0.26-0.69%) to 0.67% (0.46-0.89%). The corresponding figures for cardiovascular mortality were 0.85% (0.53-1.18%) with no adjustment and from 0.86% (0.53-1.19%) to 1.06% (0.74-1.39%) with the methods of control.
The association between air pollution and mortality is not weakened by control for influenza epidemic irrespective of the method used. To adjust for influenza epidemics, one can use methods based on respiratory mortality counts instead of counts of influenza cases if the latter are not available. However, adjustment for influenza by any method tested did not markedly alter the air pollution effect estimate.
- SourceAvailable from: Sarah B Henderson[Show abstract] [Hide abstract]
ABSTRACT: Extreme air pollution events due to bushfire smoke and dust storms are expected to increase as a consequence of climate change, yet little has been published about their population health impacts. We examined the association between air pollution events and mortality in Sydney from 1997 to 2004. Events were defined as days for which the 24h city-wide concentration of PM(10) exceeded the 99th percentile. All events were researched and categorised as being caused by either smoke or dust. We used a time-stratified case-crossover design with conditional logistic regression modelling adjusted for influenza epidemics, same day and lagged temperature and humidity. Reported odds ratios (OR) and 95% confidence intervals are for mortality on event days compared with non-event days. The contribution of elevated average temperatures to mortality during smoke events was explored. There were 52 event days, 48 attributable to bushfire smoke, six to dust and two affected by both. Smoke events were associated with a 5% increase in non-accidental mortality at a lag of 1 day OR (95% confidence interval (CI)) 1.05 (95%CI: 1.00-1.10). When same day temperature was removed from the model, additional same day associations were observed with non-accidental mortality OR 1.05 (95%CI: 1.00-1.09), and with cardiovascular mortality OR (95%CI) 1.10 (95%CI: 1.00-1.20). Dust events were associated with a 15% increase in non-accidental mortality at a lag of 3 days, OR (95%CI) 1.16 (95%CI: 1.03-1.30). The magnitude and temporal patterns of association with mortality were different for smoke and dust events. Public health advisories during bushfire smoke pollution episodes should include advice about hot weather in addition to air pollution.Environmental Research 05/2011; 111(6):811-6. DOI:10.1016/j.envres.2011.05.007 · 3.95 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Many studies have illustrated that ambient air pollution negatively impacts on health. However, little evidence is available for the effects of air pollution on cardiovascular mortality (CVM) in Tianjin, China. Also, no study has examined which strata length for the time-stratified case-crossover analysis gives estimates that most closely match the estimates from time series analysis. The purpose of this study was to estimate the effects of air pollutants on CVM in Tianjin, China, and compare time-stratified case-crossover and time series analyses. A time-stratified case-crossover and generalized additive model (time series) were applied to examine the impact of air pollution on CVM from 2005 to 2007. Four time-stratified case-crossover analyses were used by varying the stratum length (Calendar month, 28, 21 or 14 days). Jackknifing was used to compare the methods. Residual analysis was used to check whether the models fitted well. Both case-crossover and time series analyses show that air pollutants (PM(10), SO(2) and NO(2)) were positively associated with CVM. The estimates from the time-stratified case-crossover varied greatly with changing strata length. The estimates from the time series analyses varied slightly with changing degrees of freedom per year for time. The residuals from the time series analyses had less autocorrelation than those from the case-crossover analyses indicating a better fit. Air pollution was associated with an increased risk of CVM in Tianjin, China. Time series analyses performed better than the time-stratified case-crossover analyses in terms of residual checking.Science of The Total Environment 11/2010; 409(2):300-6. DOI:10.1016/j.scitotenv.2010.10.013 · 4.10 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Both influenza viruses and air pollutants have been well documented as major hazards to human health, but few epidemiologic studies have assessed effect modification of influenza on health effects of ambient air pollutants. We aimed to assess modifying effects of influenza on health effects of ambient air pollutants. We applied Poisson regression to daily numbers of hospitalizations and mortality to develop core models after adjustment for potential time-varying confounding variables. We assessed modification of influenza by adding variables for concentrations of single ambient air pollutants and proportions of influenza-positive specimens (influenza intensity) and their cross-product terms. We found significant effect modification of influenza (p < 0.05) for effects of ozone. When influenza intensity is assumed to increase from 0% to 10%, the excess risks per 10-microg/m(3) increase in concentration of O(3) increased 0.24% and 0.40% for hospitalization of respiratory disease in the all-ages group and >or= 65 year age group, respectively; 0.46% for hospitalization of acute respiratory disease in the all-ages group; and 0.40% for hospitalization of chronic obstructive pulmonary disease in the >or= 65 group. The estimated increases in the excess risks for mortality of respiratory disease and chronic obstructive pulmonary disease in the all-ages group were 0.59% and 1.05%, respectively. We found no significant modification of influenza on effects of other pollutants in most disease outcomes under study. Influenza activity could be an effect modifier for the health effects of air pollutants particularly for O(3) and should be considered in the studies for short-term effects of air pollutants on health.Environmental Health Perspectives 02/2009; 117(2):248-53. DOI:10.1289/ehp.11605 · 7.03 Impact Factor