1. Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, NCCDPHP, DRH, 4770 Buford Highway, Mailstop K-34, Atlanta, GA 30341, USA
2. Department of Obstetrics and Gynecology, Alpert Medical School of Brown University, Providence, RI 02912, USA
3. Department of Medicine, Mount Sinai School of Medicine, New York, NY 10029, USA
4. Division of Infectious Diseases, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
5. Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
6. Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, MI 48201-1998, USA