1. From the Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, Massachusetts;
2. University of Washington, Seattle, Washington;
3. Group Health Cooperative, Seattle, Washington;
4. Centers for Disease Control and Prevention, Childhood and Respiratory Diseases Branch, Atlanta, Georgia;
5. Veterans Administration Medical Center, Philadelphia, Pennsylvania;
6. Tufts University, Medford, Massachusetts;
7. Vasca, Inc, Tewksbury, Massachusetts; and
8. Channing Laboratory, Boston, Massachusetts.