Funding for this research was provided by:
Korea Centers for Disease Control and Prevention (2016-ER6401-00)
Text and Data Mining valid from 2020-01-21
Received: 11 August 2019
Accepted: 21 October 2019
First Online: 21 January 2020
: The authors declare that they have no competing interests
: Ethics approval was not required for this research.
: Not applicable.