1 Kunjal Patel and George R. Seage III are with the Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA. Sandra K. Burchett is with the Division of Infectious Diseases, Boston Children's Hospital and Harvard Medical School, Boston. Rohan Hazra is with the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD. Russell B. Van Dyke is with the Department of Pediatrics, Tulane School of Medicine, New Orleans, LA.