1. Department of Chemistry and Biochemistry and Joint Institute Food Safety and Nutrition, University of Maryland, College Park, Maryland 207421;
2. Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Morgantown, West Virginia 265052;
3. National Veterinary and Food Research Institute,3 and
4. Department of Microbiology and Epizootology, College of Veterinary Medicine,4 Helsinki, Finland;
5. Centers for Disease Control and Prevention, Atlanta, Georgia 303415; and
6. Department of Pediatrics, Rainbow Babies and Childrens Hospital, Case Western Reserve School of Medicine, Cleveland, Ohio 441066