1. New York State Department of Health, Health Science Center, State University of New York, Stony Brook 11794
2. Field Service Division, Centers for Disease Control, Atlanta, Georgia 30333
3. Epidemiology Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840
4. Laboratory of Microbial Structure and Function, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840