Acknowledgements
The authors would like to thank the Wuhan University School of Health Sciences for their generous support in reviewing the study protocol and providing local ethical approval and permission for study operations in China. We would also like to give special thanks to Rebecca Hill for her comments and insights on the manuscript.

Authors' contributions
All authors read and approved the final manuscript. MM, EH and AC designed the study, developed the research tools and implemented the pilot study; GZ, YZ and LZ made major contributions to study implementation; LF and SM developed the data analysis and interpretation plan; HT contributed to the initial analysis; HL contributed to the study implementation, data analysis and interpretation, and writing; PD edited and approved the final version.

Funding
This work was supported by the United States Agency for International Development (USAID) Emerging Pandemic Threats PREDICT project [Cooperative Agreement No. AID-OAA-A-14-00102] and the National Institute of Allergy and Infectious Diseases of the National Institutes of Health [Award No. R01AI110964]. The contents are the responsibility of the authors and do not necessarily reflect the views of USAID, the United States Government or the National Institutes of Health.

Competing interests
None declared.

Ethical approval
This study was approved by Wuhan University School of Health Sciences Medical Ethics Committee, Institutional Review Board Administration of University of California, Davis (No. 804522–6) and Hummingbird IRB (No. 2014–23).