1. S.H.E.K is at Max Plank Institute for Infection Biology, Berlin D10117, Germany.
2. S.T.C. is at Institut Pasteur, Paris, Cedex 15, 75724 France.
3. V.M. is at National Heath Laboratory Service, Johannesburg 2000, South Africa.
4. E.R. is at Harvard School of Public Health, Boston, MA 02115.
5. C.N. is at Weill Cornell Medical College, Cornell University, New York, NY 10021.