[1] Ctr Dis Control & Prevent, Influenza Div, Natl Ctr Immunizat & Resp Dis, Atlanta, GA USA
[2] Ctr Dis Control & Prevent, Epidem Intelligence Serv, Atlanta, GA USA
[3] Univ Utah, Hlth Sci Ctr, Salt Lake City, UT USA
[4] Le Bonheur Childrens Hosp, Memphis, TN USA
[5] Univ Tennessee, Ctr Hlth Sci, Memphis, TN 38163 USA
[6] Vanderbilt Univ, Sch Med, Nashville, TN 37212 USA
[7] Northwestern Univ, Feinberg Sch Med, Chicago, IL 60611 USA
[8] Emory Univ, Sch Med, Atlanta, GA USA