Funding for this research was provided by:
National Research Foundation of Korea (NRF-2017R1A2B1008420)
Text and Data Mining valid from 2018-12-05
Received: 17 January 2018
Accepted: 28 November 2018
First Online: 5 December 2018
Compliance with ethical standards
: The study was conducted in accordance with the 1964 Declaration of Helsinki and its later amendments and was approved by the Korea Centers for Disease Control and Prevention Institutional Review Board. All subjects gave their informed consent prior to their inclusion in the study.
: The authors declare that they have no conflict of interest.