Background:
Comprehensive smoke-free legislation is an effective way to protect the population from the harms of secondhand smoke (SHS) and has been implemented in many countries. Tianjin is one of the few cities in China that have passed smoke-free legislation. We investigated the impact of smoke-free legislation on acute myocardial infarction (AMI) and stroke in Tianjin.

Methods:
An interrupted time series design adjusting for underlying secular trend, seasonal pattern, population size changes and meteorology factors was conducted to analyze the impact of the smoking free law on the weekly incidence and mortality of AMI and stroke. The study period was from January 1, 2007, to December 31, 2015, with a post-ban follow-up of 3.5 years.

Results:
Following the smoke-free law implementation, there was a decline in the annual proportional change for AMI and stroke mortality. A gradual 16% (RR:0.84; 95% CI: 0.83-0.85) decrease per year in AMI mortality among in population ages ≥ 35 years and a gradual 4% (RR:0.96; 95% CI: 0.95-0.98) decrease per year in stroke mortality among 35-64 age group in Tianjin was observed. Post-ban stroke incidence immediate reductions were found in in stroke in 35-64 age group (RR:0.96; 95% CI: 0.95-0.98). AMI incidence immediate reductions were only found in females aged 35-64 (RR:0.71; 95% CI: 0.65-0.78).

Conclusions:
The smoke-free law in Tianjin was associated with gradual reductions in AMI and stroke mortality and immediate reductions in AMI and stroke incidence. The considerably modest and inconsistent effect on AMI and stroke incidence probably reflects the weak law enforcement and limitation of incidence surveillance data in Tianjin. This study reinforces the need for large-scale, effective and comprehensive smoke-free law in China.
Funding: This research was supported by China Medical Board (15-208)