[1] Univ Washington, Dept Med, Virol Res Clin, Seattle, WA 98122 USA
[2] Univ Washington, Dept Epidemiol, Seattle, WA 98122 USA
[3] Univ Washington, Dept Lab Med, Seattle, WA 98122 USA
[4] Fred Hutchinson Canc Res Ctr, Program Infect Dis, Seattle, WA 98104 USA