1 Division of Infectious Diseases, Departments of Microbiology and Immunology and Medicine, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA acasade1@jhu.edu.
2 Departments of Pediatrics and of Pathology, Microbiology, and Immunology and Elizabeth B. Lamb Center for Pediatric Research, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
3 Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA.
4 Department of Microbiology and Molecular Genetics, University of California Irvine, California, USA.
5 Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA.