1. Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD 21201, USA
2. Asociación para la Prevención y Estudio del VIH/Sida, Retalhuleu 11001, Guatemala
3. Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
4. Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD 21202, USA
5. The Mathile Institute for the Advancement of Human Nutrition, Dayton, OH 45414, USA
6. Jiann Ping Hsu College of Public Health, Georgia Southern University, Statesboro, GA 30458, USA
7. RTI International, Research Triangle Park, NC 27709, USA