The U.S. Food and Drug Administration (FDA) has released a report on its investigation of the Salmonella Typhimurium outbreak that caused 31 reported illnesses and four hospitalizations in the U.S. between June and August 2021. The FDA worked with the U.S. Centers for Disease Control and Prevention (CDC) and state partners to investigate the outbreak, which was linked through epidemiology and traceback to packaged salad greens during the summer of 2021. This outbreak is believed to be FDA’s first domestic investigation of a foodborne illness outbreak associated with leafy greens grown in a Controlled Environment Agriculture (CEA) operation. The CEA operation produces leafy greens using common commercial high density hydroponic growing techniques with deep water culture and floating raft production methods. The report released today includes an overview of the traceback investigation, investigation results, and various factors that potentially contributed to the contamination of packaged leafy greens with Salmonella.

Although a conclusive root cause was not identified, the agency identified certain conditions and practices that could result in contamination, including the presence of a different serotype of Salmonella in pond water used to grow the leafy greens, growth media storage practices, water management practices, and general sanitation practices at the CEA that were inadequate to prevent the introduction or spread of microorganisms of public health significance into the leafy greens.

FDA isolated the outbreak strain of Salmonella Typhimurium in a stormwater retention basin adjacent to the CEA farm. However, the investigation did not reveal if that stormwater retention basin was the source of the Salmonella that ultimately contaminated the leafy greens. This highlights the importance of assessing all microbial hazards, including those associated with adjacent and nearby land uses.