Four healthcare workers show symptoms after bird flu exposure BBC.comMore health-care workers in contact with Missouri bird flu patient report respiratory symptoms CNNPossible Cluster of Human Bird-Flu Infections Expands in Missouri The New York TimesMissouri investigates more possible human-to-human H5N1 avian flu spread University of Minnesota Twin CitiesBird flu casts a wider net as U.S. health officials keep drip-feeding information on Fridays Fortune