- Correspondence to Dr Peter Kegel, University Medical Center of the Johannes Gutenberg University Mainz, Institute of Occupational, Social, and Environmental Medicine, Kupferbergterrasse 17–19, Mainz 55131, Germany;
- Received November 19, 2012
- Revised November 11, 2013
- Accepted November 14, 2013
- First published December 16, 2013.
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