Funding for this research was provided by:
Beijing Natural Science Foundation (7172157)
Beijing Nova Program (Z181100006218107)
Text and Data Mining valid from 2018-09-29
Received: 17 November 2017
Accepted: 23 August 2018
First Online: 29 September 2018
Ethics approval and consent to participate
: The study was approved by the institutional ethics committees of the Academy of Military Medical Sciences of the Chinese People’s Liberation Army, Beijing, China. Because the study was epidemiological without any interventions and all the data were collected and analyzed anonymously, the requirement for informed consent was waived.
: Not applicable.
: The authors declare that they have no competing interests.
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