[1] Univ Massachusetts, Sch Med, Dept Pediat, Worcester, MA 01605 USA
[2] Univ Massachusetts, Sch Med, Dept Quantitat Hlth Sci, Worcester, MA 01605 USA
[3] Univ N Carolina, Dept Epidemiol, Gillings Sch Global Publ Hlth, Chapel Hill, NC USA
[4] Kenya Govt Med Res Ctr, Ctr Global Hlth Res, Kisumu, Kenya