The purpose of this study was to evaluate the relationship between particulate air pollution and morbidity among the Kaiser Permanente (KP) membership who reside in the Central Valley (CV) of California. The combination of the ambient air pollution data collected as part of the enhanced monitoring and the morbidity data from Kaiser Permanente provided an excellent opportunity to explore this relationship in an area with varied particulate matter (PM).
We conducted time-series analyses examining the association between daily ambient measures of PM (including PM chemical components), other criteria air pollutants (e.g., ozone, NO2, and CO), and daily admissions to the emergency room or hospitalization for respiratory and cardiovascular conditions among members of Kaiser Permanente, Northern California Region (KPNC) living in the Central Valley of California. Only those KPNC members who resided in an area where exposure could be assigned using one or more of the PM monitoring stations were included in the study. The study period was from January 1996 to December 2000.
Exposure was assigned based on each KP member's residential zip code and linked to the city where a monitoring station was in place. Morbidity data were derived from computerized data sources at Kaiser Permanente. Outcome events were classified into one of three categories: cardiovascular, acute, and chronic respiratory conditions and two types of admissions: hospitalizations and emergency room visits. Generalized additive models with non-parametric smooths were developed that first fit confounding variables to each set of outcome data. These factors included long-wave terms (time), day-of-week, temperature, and humidity.
Consistent adverse health effects were observed between a variety of air pollution metrics and acute and chronic respiratory hospitalizations and emergency room visits among KP members living in the Central Valley of California. These associations were consistent across type of analysis and type of admission (hospitalization or emergency room visit). Of the pollutants studied PM10 and PM2.5 were consistently associated with increases in hospitalizations and emergency room visits for acute and chronic respiratory conditions. To a lesser extent, CO and NO2 were associated with increases in admissions for all outcomes in our study. In contrast to the PM10 and PM2.5 results, we did not find convincing evidence of an association between the coarse fraction of PM and our outcomes. In addition, our results for cardiovascular admissions were inconsistently or not at all associated with the pollutants which were studied. Finally, some of our pollutant-outcome associations were in the opposite direction from what we expected, most notably ozone.
Stephen Van Den Eeden received his Ph.D. in Epidemiology from the University of Washington School of Public Health. He has worked as an epidemiologist for the Kaiser Foundation Research Institute in Oakland for the past ten years. In addition, Dr. Van Den Eeden is a lecturer in Epidemiology at both Stanford and Berkeley. He has performed many studies examining the association between ambient pollution and cardiovascular and respiratory morbidity and mortality in California. Results from Dr. Van Den Eeden's work help scientists and policy makers understand the relationship between different measures of particulate matter and other ambient pollutants, and their effect on human cardiovascular and respiratory health.
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