- Correspondence to Dr Laura Kurth, Respiratory Health Division, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, 1095 Willowdale Road, Morgantown, WV 26505 USA;
- Received April 5, 2016
- Revised October 3, 2016
- Accepted October 10, 2016
- First published October 24, 2016.
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