[1] Univ Maryland, Sch Med,Epidemiol Sect, VA Maryland Hlth Care Syst,Med Care Clin Ctr, Dept Epidemiol & Prevent Med,Div Healthcare Outco, Baltimore, MD 21201 USA
[2] Univ Maryland, Sch Med, Ctr Vaccine Dev, Baltimore, MD 21201 USA
[3] Univ Maryland, Sch Med, Dept Med, Div Geog Med, Baltimore, MD 21201 USA
[4] Ctr Dis Control & Prevent, Atlanta, GA USA
[5] Univ Maryland, Sch Med, Dept Pediat, Baltimore, MD 21201 USA