卫生公益性行业科研专项项目(编号201402019)%北京市卫生系统高层次卫生技术人才培养计划项目(编号2013-2-005)%国家自然科学基金项目(编号81071196)%首都卫生发展科研专项项目(编号2011-4003-01)@@@@ACKNOWLEDGMENTS This work was part of the Program on Health Nonproift Industry Research Subject(201402019)%Beijing Health System High-level Health Technical Personnel Training Program(2013-2-005)%Special Funds of the National Natural Science Foundation of China(81071196)%Capital Health Development Research Project(2011-4003-01)