1. Division of Infectious Disease Epidemiology, Pennsylvania Department of Health, Harrisburg, Pennsylvania, USA
2. Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
3. Department of Public Health Sciences, Penn State College of Medicine, Hershey, Pennsylvania, USA
4. Bureau of Laboratories, Pennsylvania Department of Health, Exton, Pennsylvania, USA
5. Pennsylvania Veterinary Laboratory, Harrisburg, Pennsylvania, USA