Air Pollution and Deaths among Elderly Residents of São Paulo , Brazil : An Analysis of Mortality Displacement Amine

Short-term exposure to air pollution has been associated with a variety of adverse health effects, such as overall, circulatory, and respiratory mortality [Anderson et al. 2007; World Health Organization (WHO) 2006, 2013]. It has been suggested that short-term exposure to air pollution only affects a frail subpopulation with an elevated risk of dying owing to its poor health conditions. Consequently, an air pollution episode could deplete this frail group and advance deaths among some by a limited number of days or weeks, followed by a period with a mortality rate that is lower than expected. This phenomenon is known as “mortality displacement” or “harvesting effect” (Schwartz 2000a; Zeger et al. 1999). It is important to identify mortality displacement for public health reasons. If air pollution–related deaths are displaced only by a few days, the public health impact measured in loss of life expectancy would be less than when deaths are brought forward by a much greater period of time (Schwartz 2000a). Because the effects of air pollution on mortality could occur on the same day of exposure or on later days, the so-called lag structures need to be investigated to quantify these effects. However, if multiple lags are used in one model, common regression models will be susceptible to collinearity problems because of the high correlation among exposures on consecutive days. The solution for this problem was the development of distributed lag models (DLMs) using smooth functions, such as polynomials, to describe the relationship between lagged exposure of multiple days (Gasparrini et al. 2010; Zanobetti et al. 2000). Recently, the investigation of lag structures has been improved through the use of DLMs by several authors in different study types (Armstrong 2006; Gasparrini et al. 2010; Gasparrini 2014; Roberts and Martin 2007; Samoli et al. 2013; Schwartz 2000b). In some time series studies, the DLM was applied to quantify a cumulative effect over multiple lagged days (Braga et al. 2001; Filleul et al. 2004; O’Neill et al. 2008; Romieu et al. 2012; Samoli et al. 2009, 2013; Schwartz 2000b), to evaluate the mortality displacement attributable to air pollution (Goodman et al. 2004; Zanobetti et al. 2000, 2002, 2003; Zanobetti and Schwartz 2008), or for a combination of both purposes. In most cases, studies that used DLM with lag structures ≤ 60 days have not found mortality displacement within this time period, which suggests that the effects of air pollution on mortality are not simply because of deaths being advanced by a few days or weeks. In these studies, effects based on single-day lags underestimate cumulative effects (Goodman et al. 2004; Zanobetti et al. 2002, 2003; Zanobetti and Schwartz 2008). A European multicity study (Zanobetti et al. 2002, 2003) estimated the effects of a 10 μg/m3 increase in particulate matter < 10 μm (PM10) and reported that nonacci dental, cardiovascular, and respiratory deaths increased 1.61% [95% confidence interval (95% CI): 1.02, 2.20], 1.97% (95% CI: 1.38, 2.55), and 4.20% (95% CI: 1.08, 7.42), respectively, for cumulative effects ≤ 40 days. In contrast, corresponding estimates for average exposures on the same day and on the previous day were only 0.70% (95% CI: 0.43, 0.97), 0.69% (95% CI: 0.31, 1.08), and 0.74% (95% CI: –0.17, 1.66), respectively. Mortality displacement in U.S. and European populations may differ from displacement in Latin America because of differences in population, health care, and other characteristics. However, to our knowledge, no studies of mortality displacement have been reported based on data from Latin America. In addition, we are not aware of studies that have analyzed mortality displacement in relation to daily time series of nitrogen dioxide (NO2) and carbon monoxide (CO) exposures. São Paulo is the largest and most developed city in Brazil, and it is also one of the most polluted cities (IEMA 2014). Recently, the Multicity Study of Air Pollution and