- Correspondence to Dr Ken Tokizawa, National Institute of Occupational Safety and Health, Nagao 6-21-1, Tama, Kawasaki, Kanagawa 214–8585, Japan;
- Received September 2, 2014
- Revised February 16, 2015
- Accepted February 21, 2015
- First published April 23, 2015.
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