Author Contributions: Dr Yang had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Yeung, Yang, Berry.
Acquisition of data: Yang.
Analysis and interpretation of data: Yeung, Yang, Berry.
Drafting of the manuscript: Yeung, Berry.
Critical revision of the manuscript for important intellectual content: Yeung, Yang, Berry.
Statistical analysis: Yeung, Yang.
Obtained funding: Berry.
Administrative, technical, or material support: Yeung, Berry.
Study supervision: Berry.
Financial Disclosures: None reported.
Funding/Support: This study was supported by the Centers for Disease Control and Prevention.
Role of the Sponsor: Employees of the Centers for Disease Control and Prevention supervised the design and conduct of the study; the collection, management, analysis, and interpretation of the data; and the preparation, review, and approval of the manuscript.
Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Additional Contributions: Mary E. Cogswell, PhD, Centers for Disease Control and Prevention, provided expert advice. No compensation was received.