IN JUNE and July 1997, simultaneous outbreaks of Escherichia coli O157:H7 infection in Michigan and Virginia were independently associated with eating alfalfa sprouts grown from the same seed lot. The outbreak strains in Michigan and Virginia were indistinguishable by molecular subtyping methods. This report summarizes the preliminary findings of the outbreak investigations.
During June 1-July 31, a total of 60 persons with E. coli O157:H7 infection were reported to the Michigan Department of Community Health (MDCH) from 16 counties throughout southern and central Michigan; in comparison, during the same period in 1996, a total of 31 infections were reported throughout the state. Of the 60 persons reported in June and July 1997, isolates from 40 (67%) persons were indistinguishable from each other by pulsed-field gel electrophoresis (PFGE) subtyping performed at the molecular laboratory of MDCH; 14 (23%) had isolates with various other PFGE patterns, and six (10%)