Irrigation water issues potentially related to the 2006 multistate E. coli O157:H7 outbreak associated with spinach

A multistate Escherichia coli O157:H7 outbreak in August and September 2006 was found to be associated with consumption of fresh bagged spinach traced to California. The California Food Emergency Response Team (CALFERT), consisting of personnel from the California Department of Public Health Food and Drug Branch (FDB) and the U.S. Food and Drug Administration (FDA) undertook an environmental investigation to determine how and why the spinach became contaminated. At the invitation of FDA and FDB, the Centers for Disease Control and Prevention (CDC) also participated in the environmental investigation. This paper presents findings from the portion of the environmental investigation focusing on environmental factors related to irrigation water that may have contributed to contamination of the spinach and hence to the outbreak. Analysis of the available data suggests that depths to groundwater and groundwater–surface water interactions may pose risks to ready-to-eat crops. These risks should be further evaluated and quantified to understand and identify the factors that contributed to this and similar outbreaks. One implication of this analysis is the need to continue to conceptually broaden the scope of produce-related outbreak investigations. Where feasible, investigation strategies should integrate possible contamination sources beyond those actually found on the farms that are identified as sources of produce involved in outbreaks.