-
AMI incidence data were obtained from the Shenzhen AMI Registry System. This system was established in January 2012 and covered all Shenzhen permanent residents. Each AMI case was reported by all the secondary and tertiary hospitals in Shenzhen [30]. The Shenzhen Center for Chronic Disease Control assessed and checked the data quality since underreporting existed in the early stage of system establishment. Therefore, we analyzed the AMI incidence data starting from May 29, 2012, when the system was stable. Stroke incidence data were obtained from the Shenzhen Stroke Registry System, established in October 2002. Its reporting procedures were similar to the AMI Registry System [31]. Since the AMI incidence data started in 2012, this was used as the start date for the stroke data. Study subjects included in- and out-patients for AMI or stroke and ambulatory patients.
The structure of these two databases is similar. They record individual information, including a unique ID, age, sex, household type (urban or rural), dates of admission and primary diagnosis, and other relevant information. The classification of AMI and stroke was based on the International Classification of Diseases, Tenth Version (ICD-10). We identified all cases with a principal diagnosis of stroke (hemorrhagic stroke: I60–I62, ischemic stroke: I63) or AMI (I21). The incidence of AMI and stroke was calculated based on the number of events. Recurrence within 28 days was not included in incidence calculations, and recurrence after 28 days was considered a new case [10,11]. The sample was restricted only to the resident population aged ≥ 35 due to the low incidence of stroke and AMI among people aged < 35.
The meteorological data on the average daily temperature and relative humidity were obtained from the Shenzhen Meteorological Bureau. The daily particulate matter with aerodynamic diameter ≤ 2.5 μm (PM2.5) concentrations (μg/m3) from 2015 to 2016 were obtained from the local Environmental Monitoring Center Station. PM2.5 data from 2012 to 2014 were replaced with Tracking Air Pollution in China (TAP, http://tapdata.org.cn/) since the local Environmental Monitoring Center Station did not monitor PM2.5 before 2015. This approach to tracking air pollution has been described elsewhere [32, 33]. Single-year population estimates by gender and age were obtained from the Shenzhen Bureau of Statistics.
-
The crude incidence rate for all AMI, hemorrhagic stroke, and ischemic stroke was calculated as the number of annually diagnosed new cases divided by the resident population. We also calculated age-standardized incidence rates using the age structure of the Shenzhen population in 2017.
A Poisson regression model with interrupted time series was used to test the immediate and gradual changes in the crude incidence rate after the smoke-free legislation. All variables in the model were established as a time series in weeks. Multiple models were fitted by sex and age groups (35–49, 50–64, and ≥ 65 years) to evaluate the effect of the law on different subgroups. The response variable of each model was the weekly number of events for the selected diseases. An indicator variable was used to define the smoke-free legislation, with 0 given to the weeks before enforcing the law and 1 given to the weeks after enforcing it. An interaction term between legislation and weeks after the law implementation was included to estimate the change in the slope of the secular trend, and the weeks were set as 0 before enforcing the law. The age group and sex-specific resident population were included as an offset variable with a fixed coefficient of 1 in each model. A linear predictor, adjusted the long-term time trend, was included to quantify the changes in population risk factors, treatment, and other secular trends [10, 11]. A Fourier series of sine and cosine terms was used to capture the seasonal pattern in the model. The study period for stroke and AMI was from January 01, 2012, to December 31, 2016, and from May 29, 2012, to December 31, 2016, respectively. In addition, the temperature (°C), relative humidity (%), and PM2.5 were adjusted in all models [12, 34]. The Poisson regression model is as follows:
$$ \begin{aligned} &{\rm{log}}\left(Y\right)={\beta }_{0}+{\beta }_{1}T+{\beta }_{2}Law+{\beta }_{3}\left(Law \times {T}{\text{'}}\right)\\ &+{\beta }_{4}{\rm{cos}}\left(\frac{2T\pi }{52.1775}\right) +{\beta }_{5}\rm{sin}\left(\frac{2T\pi }{52.1775}\right)\\ &+{\beta }_{k}\left(Tem,Hum,PM_{2.5}\right)+offset\;{\rm{log}}\left(P\right) , \end{aligned}$$ (1) where Y denotes weekly age- and sex-specific events (AMI, hemorrhagic stroke, and ischemic stroke), P is the age- and sex-specific resident population every year, T is the time variable during the study period (week, AMI: from 1 to 240, hemorrhagic stroke and ischemic stroke: from 1 to 261), T’ is the time variable (week) after law enforcement. Law represents the implementation of the smoke-free law (AMI: Law equals 0 before 93 weeks/1 after 93 weeks, stroke: Law equals 0 before 114 weeks/1 after 114 weeks). β0 is the baseline level. β1 represents the secular trend before law enforcement, β2 represents the immediate effect of the ban, β3 represents the gradual weekly effect of the ban, β4 and β5 represent seasonality in the model, βk denotes the coefficient for a set of covariates. Models were fitted separately for each age group and sex.
The effect of the smoke-free legislation was reflected by the immediate and gradual change in the incidence rate, respectively. The former was quantified as 100[exp(β2)−1], and the latter was quantified as 100[exp(52.1775×β3)−1]. In addition, the number of averted events (net post-legislation decrease) was calculated as the subtraction between the actual events and the predicted number of events without the influence of the law. All analyses were conducted in R V.4.1.0 (R Foundation for Statistical Computing, Vienna, Austria).
Ethical approval was not required as the data were deidentified, and results were presented at the group level.
-
Between January 01, 2012, and December 31, 2016, 72,945 incident ischemic strokes and 18,659 incident hemorrhagic strokes were identified among the resident population aged ≥ 35 years in Shenzhen. There were 17,431 cases of incident AMI from May 29, 2012, to December 31, 2016. The annual incidence rates were 398.9, 102.0, and 104.1 per 100,000 population for ischemic stroke, hemorrhagic stroke, and AMI, respectively. Overall, an annual increase in the age-standardized incidence rates for ischemic stroke and AMI was observed during the study period. A similar trend was also observed for hemorrhagic stroke. However, its standardized rates decreased in 2015 compared with previous years and then significantly increased rapidly in 2016 (Table 1). We calculated the average annual incidence rate of AMI and two stroke subtypes by age and gender during the study period (Table 2). Regardless of any disease, the incidence in men was higher than in women. In addition, the older the age group, the higher the incidence was. In particular, the incidence of ischemic stroke in the age group ≥ 65 years was about 48 times higher than in the age group 35–49 years.
Year Ischemic stroke incidence Hemorrhagic stroke AMI Case, n Crude annual rate
(95% CI)Standardized annual rate (95% CI) Case, n Crude annual rate
(95% CI)Standardized annual rate (95% CI) Case, n Crude annual rate
(95% CI)Standardized annual rate (95% CI) 2012 10,891 311.1 (305.3, 317.0) 281.8 (276.3, 287.4) 3,084 88.1 (85.0, 91.2) 83.6 (80.6, 86.6) 1,484* 72.7 (69.9, 75.5) 69.6 (68.8, 72.4) 2013 12,508 355.2 (349.0, 361.4) 321.0 (315.1, 326.9) 3,551 100.8 (97.5, 104.2) 95.2 (92.0, 98.5) 3,170 90.0 (86.9, 93.2) 82.5 (79.5, 85.5) 2014 14,693 412.5 (405.8, 419.1) 372.8 (366.5, 379.2) 3,716 104.3 (101.0, 107.7) 98.7 (95.5, 102.0) 3,616 101.5 (98.2, 104.8) 93.1 (89.9, 96.3) 2015 16,283 432.8 (426.2, 439.4) 391.4 (385.1, 397.7) 3,784 100.6 (97.4, 103.8) 95.5 (92.4, 98.7) 3,999 106.3 (103.0, 109.6) 97.5 (94.4, 100.7) 2016 18,570 471.5 (464.8, 478.3) 427.2 (420.7, 433.6) 4,524 114.9 (111.5, 118.2) 108.7 (105.5, 112.0) 5,162 131.1 (127.5, 134.6) 120.1 (116.7, 132.5) Total 72,945 398.9 (392.5, 405.4) − 18,659 102.0 (98.8, 105.3) − 17,431 104.1 (100.8, 107.4) − Note. *Excluding the first 21 weeks of data. Table 1. Annual incidence rate (1/100,000) of AMI and stroke among the resident population aged 35 years and older in Shenzhen from 2012 to 2016
Subgroups Ischemic stroke Hemorrhagic stroke AMI Case, n % Average incidence (95% CI) Case, n % Average incidence (95% CI) Case, n % Average incidence (95% CI) Age (years) 35–49 11,236 15.4 79.2 (75.9–82.5) 6,539 35.0 46.1 (43.6–48.6) 3,551 20.3 27.2 (25.3–29.2) 50–64 24,536 33.6 787.7 (765.7–809.6) 6,945 37.2 222.9 (211.2–234.7) 5,391 30.8 188.3 (177.6–199.1) ≥ 65 37,173 51.0 3782.0 (3697.7–3866.3) 5,175 27.7 526.5 (494.5–558.5) 7,005 40.0 775.6 (736.8–814.4) Sex Men 43,606 59.8 432.8 (423.7–441.9) 12,097 64.8 120.1 (115.3–124.8) 13,153 75.2 142.1 (136.9–147.3) Women 29,339 40.2 357.4 (348.3–366.5) 6,562 35.2 79.9 (75.6–84.3) 4,345 24.8 57.6 (53.9–61.3) Table 2. Age and sex-specific incidence rates (1/100,000) of AMI and stroke in Shenzhen from 2012 to 2016
-
For incidence rates of hemorrhagic stroke and ischemic stroke, after the enforcement of the law, the relative risk (RR) values on immediate effects were 0.94 [95% confidence interval (CI): 0.89–1.00] and 1.03 (95% CI: 1.00–1.07), respectively. These values meant that the immediate changes were not statistically significant (Table 3). An immediate decrease was seen in the age group ≥ 50 for hemorrhagic stroke, with statistical significance only in the age group 50–64. The immediate reduction in ischemic stroke was not observed in all subgroups. Regarding long-term effects, there was a 7% (RR: 0.93; 95% CI: 0.89–0.98) and 6% (RR: 0.94; 95% CI: 0.92–0.96) decrease in the above two diseases, respectively, with statistical significance. These annual, gradual changes were also observed in both genders with statistical significance. Regarding different age groups, the decreasing trends for hemorrhagic stroke and ischemic stroke were also more pronounced in the older age groups, with the largest reduction of 12% (RR: 0.88; 95% CI: 0.81–0.96) and 9% (RR: 0.91; 95% CI: 0.88–0.94) among the age group ≥ 65, respectively. For the age group 35–49, the change in the annual incidence of either disease was not significant (P > 0.05).
Subgroups Ischemic stroke incidence Hemorrhagic stroke incidence AMI incidence Immediate effect Gradual effect per annum Immediate effect Gradual effect per annum Immediate effect Gradual effect per annum RR (95% CI) RR (95% CI) RR (95% CI) RR (95% CI) RR (95% CI) RR (95% CI) Overall 1.03 (1.00–1.07) 0.94 (0.92–0.96) 0.94 (0.89–1.00) 0.93 (0.89–0.98) 0.91 (0.85–0.97) 0.94 (0.89–1.00) Age (years) 35–49 1.11 (1.02–1.20) 1.00 (0.95–1.07) 1.04 (0.94–1.15) 1.00 (0.92–1.08) 1.09 (0.94–1.26) 0.99 (0.87–1.13) 50–64 1.07 (1.01–1.13) 0.95 (0.91–0.99) 0.93 (0.84–1.03) 0.91 (0.85–0.98) 0.93 (0.83–1.05) 0.91 (0.82–1.12) ≥ 65 1.00 (0.96–1.04) 0.91 (0.88–0.94) 0.85 (0.76–0.96) 0.88 (0.81–0.96) 0.83 (0.75–0.91) 0.94 (0.86–1.04) Sex Men 1.02 (0.98–1.07) 0.93 (0.91–0.96) 0.95 (0.88–1.02) 0.94 (0.89–0.99) 0.92 (0.86–0.99) 0.92 (0.86–0.99) Women 1.05 (1.00–1.11) 0.95 (0.91–0.98) 0.93 (0.84–1.03) 0.92 (0.86–0.99) 0.88 (0.77–1.01) 1.01 (0.90–1.15) Note. *Adjusted for time trend, population, seasonality, temperature, relative humidity, and PM2.5. Table 3. Multivariate analysis* of overall, sex-, and age-specific post-legislation effects on the incidence of AMI and two subtypes of stroke, Shenzhen
After the implementation of the law, an analysis of its immediate effect showed a decrease in the AMI incidence rate, with a 9% (RR: 0.91; 95% CI: 0.85–0.97) reduction. The immediate reductions in incidence associated with the law were the highest in the age group ≥ 65, with reductions of 17% (RR: 0.83; 95% CI: 0.75–0.91). In addition, an annual change of 6% was also observed in the AMI incidence rate. However, this difference was not statistically significant (RR: 0.94; 95% CI: 0.89–1.00), which was the same for different age groups. In different genders, an annual 8% reduction (RR: 0.92; 95% CI: 0.86–0.99) was observed only among men, as detailed in Table 3.
-
Figures 1–3 show the observed and predicted trends in the weekly incidence of AMI and the two subtypes of stroke among permanent residents of Shenzhen. The weekly variation incidence rate followed a seasonal pattern, with higher incidence rates in the winter and lower rates during the summer, particularly for AMI and hemorrhagic stroke (Figure 1 and Figure 2). The health effect of the smoke-free legislation can be seen in the difference in trends between the predicted incidence rates for the counterfactual scenario (red line) and the actual rate (blue line). In sum, during the whole smoke-free legislation period of 2.7 years, there were 2,422 incidents of AMI, 2,951 incidents of ischemic strokes, and 2014 incidents of hemorrhagic strokes that had been averted due to the implementation of the law. The net decrease in AMI incidence was estimated as 11.4% during the first year, reaching 16.7% by December 2016, which also was observed in all subgroups, except that the net post-legislation reductions in the age group 35–49 and women were not apparent. Similar patterns were seen in hemorrhagic stroke and all of its subgroups. In the 2.7 years following the legislation, there was a net reduction of 15.1% for hemorrhagic stroke and only 6.9% for ischemic stroke.
Impact of Smoke-Free Legislation on Acute Myocardial Infarction and Subtypes of Stroke Incidence in Shenzhen, China, 2012–2016: An Interrupted Time Series Analysis
doi: 10.3967/bes2023.064
- Received Date: 2022-08-05
- Accepted Date: 2022-12-30
-
Key words:
- Smoke-free legislation /
- Second-hand smoke /
- Tobacco /
- Myocardial infarction /
- Stroke /
- Prevention
Abstract:
Citation: | SHI Yu Lin, XIONG Jing Fan, LIU Li Qun, ZHAO Zhi Guang, WAN Xia, PENG Ji. Impact of Smoke-Free Legislation on Acute Myocardial Infarction and Subtypes of Stroke Incidence in Shenzhen, China, 2012–2016: An Interrupted Time Series Analysis[J]. Biomedical and Environmental Sciences, 2023, 36(6): 527-536. doi: 10.3967/bes2023.064 |