- Correspondence to Dr Shu-Hong Zhu, Department of Family and Preventive Medicine, University of California, San Diego, 9500 Gilman Drive, MC 0905, La Jolla, CA 92093-0905, USA;
- Received March 11, 2014
- Revised May 8, 2014
- Accepted May 12, 2014
- First published June 16, 2014.
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