[1] Drexel Univ, Coll Med, Dept Med, Div Infect Dis & HIV Med, Philadelphia, PA 19104 USA
[2] Boston Univ, Sch Publ Hlth, Dept Epidemiol, Boston, MA 02215 USA
[3] Boston Univ, Sch Publ Hlth, Infect Dis Sect, Dept Med, Boston, MA 02215 USA
[4] Boston Univ, Sch Publ Hlth, Dept Biostat, Boston, MA 02215 USA
[5] Boston Univ, Sch Med, Gastroenterol Sect, Dept Med, Boston, MA 02215 USA