Department of Microbiology and Immunology, Geisel School of Medicine, Dartmouth College, Hanover. Department of Pediatrics, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire, USA. Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania. Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK. Tokyo Medical and Dental University, Tokyo, Japan. Section of Infectious Disease and International Health, Geisel School of Medicine, Dartmouth College, Hanover, New Hampshire, USA.