[1] Univ Calif San Francisco, San Francisco, CA 94143 USA
[2] Univ Calif Davis, Davis, CA 95616 USA
[3] Karolinska Inst, Solna, Sweden
[4] Swedish Inst Infect Dis Control, Solna, Sweden
[5] Blood Syst Res Inst, San Francisco, CA USA
[6] San Francisco VA Med Ctr, San Francisco, CA USA