1. K. Subbarao, A. Klimov, J. Katz, H. Regnery, H. Hall, C. Bender, J. Huang, M. Hemphill, T. Rowe, M. Shaw, X. Xu, K. Fukuda, N. Cox, Influenza Branch, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
2. W. Lim, Government Virus Unit, Queen Mary Hospital, Hong Kong, China.
3. M. Perdue and D. Swayne, Southeast Poultry Research Laboratory, Agriculture Research Service, U.S. Department of Agriculture, Athens, GA 30605, USA.