1. Wadsworth Center, New York State Department of Health, and Department of Environmental Health Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201-0509, Department of Veterinary & Animal Sciences, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, and 3M Medical Department, St. Paul, Minnesota 55144