1. Department of Pediatrics, Division of Pediatric Infectious Disease, University of Washington, Seattle, Washington 98195.
2. Instituto de Medicina Tropical, Universidad Mayor Nacional de San Marcos, Lima, Perú.
3. Instituto Materno-Perinatal, Lima, Perú.
4. Department of Biostatistics, University of Washington, Seattle, Washington 98195.
5. Department of Laboratory Medicine, University of Washington, Seattle, Washington 98195.