Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. michiel.van.boven@rivm.nl|Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. michiel.van.boven@rivm.nl|Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. michiel.van.boven@rivm.nl|Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. michiel.van.boven@rivm.nl|Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. michiel.van.boven@rivm.nl