RESEARCH REPORT The National Morbidity, Mortality, and Air Pollution Study Part II: Morbidity and Mortality from Number 94, Part II June 2000 Air Pollution in the United States Jonathan M Samet, Scott L Zeger, Francesca Dominici, Frank Curriero, Ivan Coursac, Douglas W Dockery, Final Joel Schwartz, and Antonella Zanobetti Version Includes a Commentary by the Institute’s Health Review Committee HEALTH The Health Effects Institute, established EFFECTS in 1980, is an independent and unbiased INSTITUTE source of information on the health effects of motor vehicle emissions. HEI supports research on all major pollutants, including regulated pollutants (such as carbon monoxide, ozone, nitrogen dioxide, and particulate matter) and unregulated pollutants (such as diesel engine exhaust, methanol, and aldehydes). To date, HEI has supported more than 200 projects at institutions in North America and Europe and has published over 100 research reports. 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STATEMENT Synopsis of Research Report 94, Part II The National Morbidity, Mortality, and Air Pollution Study: Morbidity and Mortality from Air Pollution in the United States BACKGROUND population size and availability of PM10 data from the Epidemiologic time-series studies conducted in a US Environmental Protection Agency=s Aerometric number of cities have identified, in general, an associ- Information Retrieval System (AIRS) database, and to ation between daily changes in concentration of apply the same statistical procedures to all locations. ambient particulate matter (PM) and daily number of Dr Jonathan Samet and his colleagues at Johns deaths (mortality). Increased hospitalization (a mea- Hopkins University conducted a time-series study of sure of morbidity) among the elderly for specific mortality effects in large US cities representing various causes has also been associated with PM. These levels of PM10 and gaseous pollutants. In their anal- studies have raised concerns about public health ysis, the investigators first estimated risk in each city effects of particulate air pollution and have contrib- using the same method and then combined these uted to regulatory decisions in the United States. results systematically to draw more information than However, scientists have pointed out uncertainties any single city could provide. The 20 and 90 largest that raise questions about the interpretation of these cities were analyzed for effects of PM10 and other pol- studies. lutants on mortality; the 90 largest cities were ana- lyzed for possible modification of PM effects among One limitation to previous time-series studies of 10 cities by factors other than air pollutants. Dr Samet=s PM and adverse health effects is that the evidence for coinvestigators at Harvard University also applied a an association is derived from studies conducted in unified statistical method, although different from the single locations using diverse analytic methods. Sta- one used in the mortality analysis, to 14 cities with tistical procedures have been used to combine the daily PM data to examine effects on hospitalization results of these single location studies in order to pro- 10 among those 65 years of age or older. duce a summary estimate of the health effects of PM. Difficulties with this approach include the process by which cities were selected to be studied, the different RESULTS AND IMPLICATIONS analytic methods applied to each single study, and the NMMAPS has made a substantial contribution in variety of methods used to measure or account for addressing major limitations of previous studies. The variables included in the analysis. These individual mortality analysis used one analytic approach to studies were also not able to account for the effects of examine the PM10 effect in many cities that cover a gaseous air pollutants in a systematic manner. wide geographic area and have varying levels of dif- ferent air pollutants. The results of both the 20 cities APPROACH and 90 cities analyses are generally consistent with an average approximate 0.5% increase in overall mor- HEI funded the National Morbidity, Mortality, and tality for every 10 mg/m3 increase in PM measured Air Pollution Study (NMMAPS) to characterize the 10 the day before death. This effect was slightly greater effects of airborne particles less than 10 mm in aerody- for deaths due to heart and lung disease than for total namic diameter (PM10) alone and in combination with deaths. Effects of PM measured on the day of death gaseous air pollutants in a consistent way, in a large 10 or 2 days before did not vary substantially from one number of cities. The study was designed to select multiple locations based on the specific criteria of another for total or for heart and lung deaths. The This Statement, prepared by the Health Effects Institute, summarizes a research project funded by HEI since 1996 and conducted by Dr Jonathan M Samet of Johns Hopkins University School of Public Health, Baltimore MD. The following Research Report contains a preface, the detailed Investigators’ Report, Part II, and a Commentary on Part II prepared by a panel of the Institute’s Health Review Committee. Research Report 94, Part II PM10 effect on mortality also did not appear to be The morbidity analysis also used a unified analytic affected by other pollutants in the model. method to examine the association of PM10 with hos- Although individual estimates for each of the 90 pitalization of those 65 years of age or older in 14 cities varied, as expected, the strength of the analysis cities with daily PM10 measurements. The results was in its ability to combine data from nearby cities in were consistent with an approximate 1% increase in admissions for cardiovascular disease and about a 2% a particular region to estimate a PM10 effect. Com- bining the data in this systematic way provided addi- increase in admissions for pneumonia and chronic m 3 tional statistical power to the analysis that is not obstructive pulmonary disease for each 10 g/m available in single-city analyses. Some differences in increase in PM10. A greater estimate of effect on hos- m PM effect on mortality were seen by region of the pitalizations at lower concentrations (less than 50 g/ 10 3 US: for the 90 cities, the largest effect was evident in m ) was found for the three diagnoses considered, but the Northeast. The investigators did not identify any the meaning of these findings should await comple- factor or factors that might explain these differences. tion of concentration-response analyses for mortality This analysis is an important first step, and further now under way using data from 20 cities. evaluation of the reasons for these regional differences NMMAPS has made substantial contributions to our will advance our understanding of the association understanding of the relationship between exposure to between PM10 and mortality. The heterogeneity of PM10 and health effects. Further analyses in these data- effect across cities offers the potential to identify fac- bases of regional differences, the effects on morbidity tors that could influence the effects of PM10 on health and mortality combined, and concentration-response and thus provide valuable insights into the mecha- relationships will enhance our understanding. nisms by which PM10 causes adverse health effects. Copyright © 2000 Health Effects Institute, Cambridge MA. Printed at Flagship Press, North Andover MA. Library of Congress Catalog Number for the HEI Report Series: WA 754 R432. The paper in this publication meets the minimum standard requirements of the ANSI Standard Z39.48-1984 (Permanence of Paper) effec- tive with Report Number 21, December 1988, and with Report Numbers 25, 26, 32, 51, 65 Parts IV, VIII, and IX, and 91 excepted. These excepted Reports are printed on acid-free coated paper. CONTENTS Research Report 94 The National Morbidity, Mortality, and Air Pollution Study Part II: Morbidity and Mortality from Air Pollution in the United States Jonathan M Samet, Scott L Zeger, Francesca Dominici, Frank Curriero, Ivan Coursac, Douglas W Dockery, Joel Schwartz, and Antonella Zanobetti Departments of Epidemiology and Biostatistics, Johns Hopkins University School of Public Health, Baltimore, Maryland, and Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts HEI STATEMENT This Statement, prepared by the Health Effects Institute, is a nontechnical summary of the Investigators’ Report and the Health Review Committee’s Commentary. PREFACE Origins and Objectives . 1 Structure of Investigators’ Report . 2 Study Participants and Conduct . 2 Acknowledgments . 2 Review of Investigators’ Report . 2 References . 4 INVESTIGATORS’ REPORT When an HEI-funded study is completed, the investigators submit a final report. This Investigators’ Report is first examined by three outside technical reviewers and a biostatistician. The report and the reviewers’ comments are then evaluated by members of the HEI Health Review Committee, who had no role in selecting or managing the project. During the review process, the investigators have an opportunity to exchange comments with the Review Committee and, if necessary, revise the report. Overview. 5 Second-Stage Assessment of Confounding Project Objectives. 5 and Effect Modification . 34 Introduction to NMMAPS Part II . 6 Results . 35 Background . 6 Base Models . 37 Mortality . 8 Overall Effects of PM10 .