1. From the Epidemic Intelligence Service, State Branch, Division of Applied Public Health Training, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia;
2. Bureau of Communicable Diseases, Wisconsin Division of Public Health, Madison, Wisconsin;
3. Department of Epidemiology and Biostatistics, Marshfield Epidemiologic Research Foundation, Marshfield, Wisconsin; and
4. Childhood and Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia.