1. From the Slone Epidemiology Unit, School of Public Health, Boston University School of Medicine, Brookline, Massachusetts;
2. Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia;
3. Epidemic Intelligence Service, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia;
4. Center for American Indian and Alaskan Native Health, Johns Hopkins University School of Public Health, Baltimore, Maryland; and the
5. National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia.