[1] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Int Hlth, Ctr Amer Indian Hlth, Baltimore, MD 21205 USA
[2] Ctr Dis Control & Prevent, Gastroenteritis & Resp Viruses Lab Branch, Div Viral Dis, Natl Ctr Immunizat & Resp Dis, Atlanta, GA USA
[3] Ctr Dis Control & Prevent, Epidemiol Branch, Div Viral Dis, Natl Ctr Immunizat & Resp Dis, Atlanta, GA USA