Funding for this research was provided by:
Bill and Melinda Gates Foundation (51914)
the Health Reseach fund of Jiangsu provincial commission of health and family planning (Z201505)
Received: 28 February 2018
Accepted: 9 January 2019
First Online: 18 January 2019
Ethics approval and consent to participate
: The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the Chinese Centers for Disease Control and Prevention (Reference number not appropriate). This study used only routine data and did not involve any human participation; therefore, the application for waiving informed consent was accepted by the Ethics Committee.
: Not applicable.
: The authors declare that they have no competing interests.
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