1. Department of Epidemiology, School of Public Health, University of Michigan , Ann Arbor, Michigan , USA
2. Health Center Sócrates Flores Vivas, Ministry of Health , Managua , Nicaragua
3. Sustainable Sciences Institute , Managua , Nicaragua
4. Laboratorio Nacional de Virología, Centro Nacional de Diagnóstico y Referencia, Ministry of Health , Managua , Nicaragua
5. Biostatistics Division, College of Public Health, The Ohio State University , Columbus, Ohio , USA