1. Department of Epidemiology, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina , USA
2. Centro de Investigación en Enfermedades Tropicales, Facultad de Microbiología, Universidad de Costa Rica , San José , Costa Rica
3. Universidad Tecnológica La Salle Facultad de Ingeniería, , León , Nicaragua
4. Department of Family Medicine, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina , USA
5. Department of Pediatrics, Larsson-Rosenquist Foundation Mother-Milk-Infant Center of Research Excellence, Human Milk Institute, University of California San Diego , La Jolla, California , USA
6. Division of Viral Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia , USA
7. Department of Microbiology and Immunology, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina , USA