Author Contributions
Conceived and designed the study: Desheng Zhai, Shi Wu Wen, Ravi Retnakaran. Participated in data collection and analysis: Ying Zhao, Na Wang, Mingcan Li, Yuan Yuan, Ruiling Zhang. Wrote the first draft of the manuscript: Ying Zhao. All authors contributed to refinement of the study protocol and contributed to, and approved, the final manuscript. Author R. Zhang and D. Zhai have full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.