The U.S. Food and Drug Administration (FDA) has released a report on its investigation of the Salmonella Newport outbreak that caused more than 1,600 reported illnesses in the U.S. and Canada between June and October 2020.

The outbreak was linked through epidemiology and traceback to whole red onions supplied by Thomson International Inc., headquartered in Bakersfield (Southern San Joaquin Valley) with additional operations in Holtville (Imperial Valley), California.

The outbreak is the largest Salmonella foodborne illness outbreak in over a decade. The report released includes an overview of the traceback investigation, subsequent on-site interviews, visual observations of the growing fields, and environmental sampling, and various factors that potentially contributed to the contamination of red onions with Salmonella.

Although a conclusive root cause could not be identified, several potential contributing factors to the 2020 Salmonella outbreak linked to red onions were identified.

These include: potentially contaminated sources of irrigation water; sheep grazing on adjacent land; signs of animal intrusion, including scat (fecal droppings), and large flocks of birds that may spread contamination; and food contact surfaces that had not been inspected, maintained or cleaned as frequently as necessary to protect against the contamination of produce.

In sampling conducted in Holtville, CA, the FDA found Salmonella Newport in 10 water (irrigation, seepage, and drainage) and one sediment subsamples. However, the whole-genome sequencing of these samples did not match the outbreak strain.

Although a conclusive root cause could not be identified, several potential contributing factors to the 2020 red onion outbreak were identified, including a leading hypothesis that contaminated irrigation water used in a growing field in Holtville, CA may have led to contamination of the onions.