1. Consultant, Pan American Health Organization, Washington, D.C., United States of America.
2. Send correspondence to: Nancy K. Russell, nc3russell@yahoo.com
3. George Mason University, Fairfax, VA, United States of America.
4. Pan American Health Organization, Washington, D.C., United States of America.
5. Public Health Department, University of Brasília, Brasília, D.F., Brazil.