1. Departments of Global Health, Medicine, and Epidemiology, University of Washington, Seattle, Washington 98104, USA;
2. Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA;
3. Department of Obstetrics, Gynecology, and Reproductive Sciences and Department of Microbiology and Molecular Genetics, University of Pittsburgh, Magee-Womens Research Institute, Pittsburgh, Pennsylvania 15213, USA;