Massachusetts General Hospital waited four days before alerting Boston health authorities that a wave of gastrointestinal illness was sweeping through patients and staff. The delay is an apparent violation of rules requiring prompt reporting of suspected infectious disease clusters. Anita Barry, MD, the city's director of communicable disease control, said that the hospital "dropped the ball" in failing to report the illnesses sooner. Her agency will have discussions with the hospital about preventing such episodes in the future, she said.