[1] Univ Zurich, Childrens Hosp, Div Infect Dis, CH-8032 Zurich, Switzerland
[2] Univ Zurich, Inst Med Virol, CH-8028 Zurich, Switzerland
[3] Univ Zurich, Childrens Hosp, Dept Pediat, Zurich, Switzerland
[4] Univ Zurich, Dept Med Microbiol, CH-8028 Zurich, Switzerland