Center for Biomedical Informatics Research, Department of Medicine, Stanford University, Stanford, California, United States of America.|Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio, United States of America.|UCLA AIDS Institute and Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, Los Angeles, California, United States of America.|Center for Biomedical Informatics Research, Department of Medicine, Stanford University, Stanford, California, United States of America.