About the Authors
Laboratory Branch, Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: HZ WH WMS. Performed the experiments: HZ HJ AS. Analyzed the data: HZ WH WMS. Wrote the paper: HZ WH WMS.