[1] Univ Texas, Hlth Sci Ctr, Dept Pediat, San Antonio, TX 78284 USA
[2] Univ Texas, Hlth Sci Ctr, Dept Microbiol, San Antonio, TX 78284 USA
[3] Yale Univ, Sch Med, Dept Pediat, New Haven, CT 06510 USA
[4] Yale Univ, Sch Med, Dept Epidemiol & Publ Hlth, New Haven, CT 06510 USA
[5] Yale New Haven Hosp, Dept Hosp Epidemiol, New Haven, CT 06504 USA