1. Center for Child Health Care Studies, Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston, Massachusetts
2. Division of Infectious Diseases, Children's Hospital Boston, Boston, Massachusetts
3. Department of Population and International Health, Harvard Center for Population and Development Studies, Harvard School of Public Health, Boston, Massachusetts
4. International Health Institute and Department of Pediatrics, Brown University, Providence, Rhode Island
5. Clinical Research Institute, Tufts–New England Medical Center, Boston, Massachusetts