1 Department of Mechanical Engineering, Stanford University, Stanford, Boston, Mass.
2 Department of Mechanical Engineering, Stanford University, Stanford, Boston, Mass; Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, Mass.
3 Department of Mechanical Engineering, Stanford University, Stanford, Boston, Mass; Department of Pathology, Stanford University School of Medicine, Stanford, Calif; Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, Calif. Electronic address: sgalli@stanford.edu.