- Correspondence to Dr Matthew Keifer, National Farm Medicine Center, Marshfield Clinic Research Foundation, 1000 N Oak Ave ML-1, Marshfield, WI 54449, USA;
- Received May 8, 2014
- Revised August 12, 2014
- Accepted August 20, 2014
- First published September 4, 2014.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.