1. Minnesota Department of Health, Infectious Disease Epidemiology, Prevention and Control Division, St. Paul, MN, USA
2. Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Institute, Marshfield, WI, USA
3. Immunization Services Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA
4. National Farm Medicine Center, Marshfield Clinic Research Institute, Marshfield, WI, USA