- Correspondence to Dr Wen Qi Gan, Department of Preventive Medicine and Environmental Health, University of Kentucky College of Public Health, 111 Washington Avenue, Suite 215, Lexington, KY 40536, USA;
- Received December 16, 2014
- Revised August 20, 2015
- Accepted August 31, 2015
- First published September 15, 2015.
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