[1] Univ S Carolina, Sch Med, Dept Epidemiol & Biostat, Columbia, SC 29204 USA
[2] Univ S Carolina, Sch Med, Dept Pathol, Columbia, SC 29204 USA
[3] Med Univ S Carolina, Sch Nursing, Charleston, SC 29425 USA
[4] Univ Arkansas Med Sci, Dept Obstet & Gynecol, Little Rock, AR 72205 USA