- Correspondence to Dr Yoosoo Chang, Department of Occupational and Environmental Medicine, Kangbuk Samsung Hospital, 108 Pyung dong, Jongro-Gu, Seoul, 110-746, Republic of Korea;
- Received 15 August 2014
- Revised 8 January 2015
- Accepted 15 January 2015
- Published online 2 March 2015.
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