- Correspondence to Dr Shu-Hong Zhu, Department of Family Medicine and Public Health, University of California, San Diego, 9500 Gilman Drive, MC 0905, La Jolla, CA 92093-0905, USA;
- Received March 5, 2015
- Revised June 15, 2015
- Accepted July 7, 2015
- First published August 17, 2015.
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