[1] Broad Inst MIT & Harvard, Cambridge, MA USA
[2] Univ Maryland, Dept Comp Sci, College Pk, MD 20742 USA
[3] Univ Maryland, Ctr Bioinformat & Computat Biol, College Pk, MD 20742 USA
[4] Univ Michigan, Dept Microbiol & Immunol, Ann Arbor, MI 48109 USA
[5] Harvard Univ, Sch Publ Hlth, Dept Biostat, Boston, MA 02115 USA