doi:10.1017/S0007114515001543, Published by Cambridge University Press, 12 September, 2015.
As Haihong Zhang is the principal researcher of this study, we would like to assign her as the corresponding author. Shengmin Lv is no longer the corresponding author.
Corresponding author: HH. Zhang, Shijiazhuang Municipal Center for Disease Prevention and Control, No. 3, Likang Street, Shijiazhuang City, 050011, Hebei Province, People’s Republic of China. Fax: 86 311 86035727. Email: firstname.lastname@example.org
The authors apologise for this error.