Scientists may have cracked the mystery surrounding the cause of the pervasive gastroen-teritis that afflicts nursing home residents. Researchers at the National Institute of Allergy and Infectious Diseases have identified a group of Norwalk-like viruses as the leading cause of diar-rheal infections in Maryland nursing homes, according to a study appearing in a recent issue of The Journal of Infectious Diseases. Symptoms of the illnessincludevomiting,diarrhea,abdominalcramps, fever, chills and headache. NIAID researchers are now working on a test to diagnose the infection.