Biostatistics Department and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.|Department of Mathematics, Stockholm University, Stockholm, Sweden.|Center for Inference and Dynamics of Infectious Diseases, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America.|Biostatistics Department and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.