Reduced Hospitalizations for Acute Myocardial Infarction After Implementation of a Smoke-Free Ordinance --- City of Pueblo, Colorado, 2002--2006

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Exposure to secondhand smoke (SHS) has immediate adverse cardiovascular effects, and prolonged exposure can cause coronary heart disease (1). Nine studies have reported that laws making indoor workplaces and public places smoke-free were associated with rapid, sizeable reductions in hospitalizations for acute myocardial infarction (AMI) (2--7). However, most studies examined hospitalizations for 1 year or less after laws were implemented; thus, whether the observed effect was sustained over time was unknown. The Pueblo Heart Study examined the impact of a municipal smoke-free ordinance in the city of Pueblo, Colorado, that took effect on July 1, 2003 (3). The rate of AMI hospitalizations for city residents decreased 27%, from 257 per 100,000 person-years during the 18 months before the ordinance's implementation to 187 during the 18 months after it (the Phase I post-implementation period).* This report extends that analysis for an additional 18 months through June 30, 2006 (the Phase II post-implementation period). The rate of AMI hospitalizations among city residents continued to decrease to 152 per 100,000 person-years, a decline of 19% and 41% from the Phase I post-implementation and pre-implementation period, respectively. No significant changes were observed in two comparison areas. These findings suggest that smoke-free policies can result in reductions in AMI hospitalizations that are sustained over a 3-year period and that these policies are important in preventing morbidity and mortality associated with heart disease. This effect likely is mediated through reduced SHS exposure among nonsmokers and reduced smoking, with the former making the larger contribution (4,6,7).

Two control sites were selected for comparison with the city of Pueblo: 1) the area of Pueblo County outside the city of Pueblo limits and 2) El Paso County, including Colorado Springs, the most populous city in this county. The city of Pueblo and Colorado Springs are located approximately 45 miles apart (Figure 1). Neither of the control sites had smoke-free laws in place before or during the study periods. Based on data from the Behavioral Risk Factor Surveillance System, the adult smoking prevalence for Pueblo County (including the city of Pueblo) and El Paso County during 2002--2003 was 25.9% (95% confidence interval [CI] = 20.2%--31.6%) and 17.4% (CI = 14.5%--20.2%), respectively. The corresponding prevalences for 2004--2005 were 20.6% (CI = 15.4%--25.8%) and 22.3% (CI = 19.3%--25.4%). Separate smoking prevalence estimates were not available for the city of Pueblo.

Persons with recognized AMIs that occur in the city of Pueblo and Pueblo County receive care at two hospitals, Parkview Medical Center and St. Mary-Corwin Medical Center, both located within the city of Pueblo. Persons with recognized AMIs that occur in El Paso County receive care at two other hospitals, Penrose Hospital and Memorial Hospital, both located in Colorado Springs. Data on AMI hospitalizations were drawn from electronic Colorado Hospital Association administrative data. These data included admission date, primary diagnosis code (based on International Classification of Diseases, Ninth Revision codes 410.0--410.9), sex, age, postal code of residence, and hospital name. No other patient-level data, including smoking status, were available. U.S. Census Bureau population data for 2006 were used as denominators in calculating AMI hospitalization rates. A more extensive description of the study's methodology has been published previously (3). AMI hospitalization rates among residents of the city of Pueblo, the area of Pueblo County outside the city of Pueblo limits, and El Paso County were compared across three periods: 0--18 months before the smoke-free law took effect (pre-implementation period), 0--18 months after this date (Phase I, post-implementation period), and 19--36 months after this date (Phase II, post-implementation period), for a total of 54 months. Rates were compared between periods using a chi-square test. Relative rates (RRs) were calculated as the ratios of AMI rates between two periods. Data presented in this report were not adjusted for seasonality because a season-adjusted analysis of Phase I versus the pre-implementation period found that the adjustment did not significantly change the findings (3).

During Phase II, AMI hospitalizations among residents of the city of Pueblo continued to decrease (Figure 2). AMI hospitalization rates differed significantly across all three periods within the city of Pueblo (p<0.001). The rate of AMI hospitalization among residents in the city of Pueblo in the Phase II post-implementation period was 152 per 100,000 person-years, compared with 187 per 100,000 person-years in the Phase I post-implementation period, for an RR of 0.81 (CI = 0.67--0.96) (Table). In contrast, no significant change was observed for residents of the area of Pueblo County outside the city of Pueblo limits (139 per 100,000 person-years versus 115 per 100,000 person-years; RR = 1.21 [CI = 0.80--1.62]) or for residents of El Paso County (149 per 100,000 person-years versus 150 per 100,000 person-years; RR = 0.99 [CI = 0.91--1.08]) during the same period. The RR for AMI hospitalizations in the city of Pueblo in the Phase II post-implementation period compared with the pre-implementation period (rate = 257 per 100,000 person-years) was 0.59 (CI = 0.49--0.70). In contrast, RRs for the area of Pueblo County outside the city of Pueblo limits and for El Paso County for the same period were 1.03 (CI = 0.68--1.39) and 0.95 (CI = 0.87--1.03), respectively; the pre-implementation period rates were 135 per 100,000 person-years and 157 per 100,000 person-years, respectively. Within each site, the distribution of AMI patients by age and sex was unchanged over time.

To further examine whether the change in AMI rates could be attributed to pre-existing secular trends, AMI rates were examined for all three sites for three 18-month periods immediately preceding the pre-implementation phase. No statistically significant secular trend occurred in any of the three sites before July 1, 2003.

To ensure that the observed change in the city of Pueblo was not attributable to undercounting fatal AMIs post-implementation, the number of AMI deaths for the city of Pueblo were obtained from the Health Statistics Section of the Colorado Department of Public Health and Environment. After accounting for AMI deaths in a conservative manner (by assuming that all fatal AMIs occurred in patients who failed to reach the hospital) and adding these numbers to the hospital AMI admission data, the RR for the city of Pueblo remained statistically significant at 0.82 (CI = 0.64--0.97) from the Phase II to Phase I post-implementation periods and at 0.66 (CI = 0.55--0.77) from Phase II post-implementation to the pre-implementation period.

Reported by: RN Alsever, MD, Parkview Medical Center; WM Thomas, PhD, St. Mary-Corwin Medical Center; C Nevin-Woods, DO, R Beauvais, S Dennison, R Bueno, Pueblo City-County Health Dept; L Chang, PhD, Colorado State Univ-Pueblo; CE Bartecchi, MD, Univ of Colorado School of Medicine. S Babb, MPH, A Trosclair, MS, M Engstrom, MS, T Pechacek, PhD, R Kaufmann, PhD, Office on Smoking and Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note:

Evidence from animal and human studies indicates that SHS exposure can produce rapid adverse effects on the functioning of the heart, blood, and vascular systems that increase the risk for a cardiac event (1). Relevant mechanisms include effects on platelet function, endothelial function, and inflammation. Epidemiologic and laboratory data indicate that the risk for heart disease and AMI increase rapidly with relatively small doses of tobacco smoke, such as those received from SHS, and then continue to increase more slowly with larger doses (1,8,9). Evidence also suggests that the acute effects of SHS exposure might be rapidly reversible (8,9).

Eliminating smoking in indoor spaces is the only way to fully protect nonsmokers from SHS (1). Previous studies have found that SHS exposure decreases substantially among nonsmoking employees of restaurants and bars and among nonsmoking adults in the general public after implementation of smoke-free laws (1,5,7,10). Compliance with smoke-free laws typically reaches high levels rapidly and then increases further over time (1,5). In addition, smoke-free laws are associated with increased adoption of no-smoking rules in private homes (1,10). Smoke-free policies have been found to prompt some smokers to quit smoking (1); because active smoking is a major risk factor for heart disease and AMI, this effect also would be expected to reduce heart disease and AMI rates at a population level. The continued decrease in AMI hospitalizations observed in this study might be a result of a combination of 1) the immediate reduction in SHS exposure among nonsmokers that occurred when the city of Pueblo smoke-free ordinance was implemented, 2) further reductions in this exposure that occurred because of increased compliance with the ordinance and increased adoption of smoke-free home rules over time, and 3) increased quitting among smokers as a result of the ordinance and associated changes in social norms.

In addition to the previous study conducted in the city of Pueblo (3), eight other published studies have reported that smoke-free laws were associated with rapid, sizeable reductions in hospitalizations for AMI (2,4--7). The current study adds to the previous evidence by documenting this effect in a relatively large population and by demonstrating that the effect was sustained over an extended period. A meta-analysis of seven of the previous eight studies and one unpublished study yielded a pooled estimate of a 19% (CI = 14%--24%) reduction in AMI hospitalization rates after implementation of smoke-free laws (2). Three studies have suggested that these reductions are more pronounced among nonsmokers than among smokers (4,6,7). For example, one study that included objective confirmation of patients' smoking status reported reductions of 21%, 19%, and 14% in the number of hospitalizations for acute coronary syndrome among never smokers, former smokers, and current smokers, respectively, in the year after implementation of a comprehensive national smoke-free law, with the decrease in hospitalizations among nonsmokers accounting for 67% of the total decrease (7).

The findings in this report are subject to at least four limitations. First, because no data were available on whether study subjects were nonsmokers or smokers, determining what portion of the observed decrease in hospitalizations was attributable to reduced SHS exposure among nonsmokers and what portion was attributable to increased quitting among smokers was not possible. The prevalence of smoking decreased in Pueblo County as a whole, but the difference over time was not statistically significant. Second, the study did not directly document reductions in SHS exposure among nonsmokers after the city of Pueblo smoke-free law took effect, although studies elsewhere have reported such reductions (1,5,7,10). Third, individual residences were assigned based on postal codes, which might have resulted in a small amount of misclassification (3); however, misclassifying residents' exposure to the city of Pueblo smoke-free ordinance would result in underestimating the effect of this ordinance. In addition, residents of the area of Pueblo County outside the city of Pueblo limits might work in workplaces or patronize restaurants or bars in the city of Pueblo, or vice versa; again, this would bias findings toward the null. Finally, the ecologic nature of this study precludes definite conclusions about the extent to which the observed decline in AMI hospitalizations in the city of Pueblo was attributable to the smoke-free ordinance. To the extent that any unmeasured factors influenced rates, the findings described in this report might overestimate or underestimate the actual effect. AMI hospitalization rates initially were substantially higher in the city of Pueblo than in the two comparison areas, suggesting that these areas might not be fully comparable to the intervention site because of demographic and other differences. However, no significant changes in the manner in which AMI patients were diagnosed, treated, or transported occurred in the three study sites during the study period. Future studies could further expand the evidence base by including information on the smoking status of AMI patients and biomarkers (e.g., cotinine and troponin) for objective measurement of SHS exposure and case ascertainment, as was done in one recent study (7).

The Phase I study findings suggested that the city of Pueblo's smoke-free ordinance led to a rapid decrease in AMI hospitalizations. The findings described in this report suggest that the initial decrease in AMI hospitalizations observed immediately after the implementation of comprehensive smoke-free laws continued over time. These findings provide support for considering smoke-free policies an important component of interventions to prevent heart disease morbidity and mortality.

This report is based, in part, on contributions by MJ Krantz, MD, B Bucher Bartelson, PhD, and RO Estacio, MD, Colorado Prevention Center, Denver, Colorado.

References

* Some of the AMI hospitalization admission figures, AMI hospitalization admission rates, relative rates, and relative rate confidence intervals calculated for this analysis differ from those previously published (3) because of receipt of routinely amended coding data from the Colorado Hospital Association.

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