1. Elson S. Floyd College of Medicine, Washington State University, Richland, Washington, United States of America.
2. Send correspondence to Jose Echaiz at jose.echaiz@wsu.edu
3. Unit of Epidemiology, HIV, and STDs, School of Public Health and Administration, Universidad Peruana Cayetano Heredia, Lima, Peru.
4. Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia, United States of America.