1. Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena, CA, USA;
2. Division of Research, Kaiser Permanente Northern California, Oakland, CA, USA;
3. Department of Obstetrics and Gynecology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA;
4. Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine at UCLA;
5. Department of Epidemiology, UCLA Fielding School of Public Health, Los Angeles, CA, USA;
6. San Francisco General Hospital, University of California, San Francisco, CA, USA;
7. Department of Medicine, University of California, San Francisco, CA, USA;
8. Los Angeles Medical Center, Kaiser Permanente Southern California, Los Angeles, CA, USA;
9. Department of Pathology and Laboratory Medicine, School of Medicine, University of California, Los Angeles, CA, USA