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Déjà vu all over again – Romaine lettuce contaminated with E. coli from irrigation water

By: Brian Grochowski

Back in June 2018, 210 people were infected with E. coli O157:H7 and 96 people were hospitalized, and five people died having consumed contaminated romaine lettuce. The source of contamination was found to be the canal water used to irrigate the lettuce. Fewer than six months after that outbreak, a similar event has occurred with the blame resting again on contaminated irrigation water.

In November 2018, Adam Bros. Farming, Inc. located in Santa Barbara County recalled red leaf lettuce, green leaf lettuce and cauliflower products over concerns of E. coli O157:H7 contamination. The latest information suggests that the source, once again, appears to be the nearby reservoir that is used to provide the irrigation water.

Hills of Lettuce

While contamination can be introduced at many different points throughout the supply chain, contaminated irrigation water seems to be a recurring theme. This is a result of farms using nearby untreated water sources like rivers, lakes and ponds. Perhaps it’s worth taking a closer look at the Food Safety Modernization Act (FSMA) produce safety rule?

The FDA final rule on produce safety has established some guidelines for irrigation water and do utilize E. coli as the indicator organism. E. coli may be present in the irrigation water so long as the geometric mean (GM) is <126CFU/100ml and the statistical threshold (STV) is <410CFU/100ml. For untreated surface water, the STV and GM are determined based on a collection of at least 20 samples over a two to four-year period. Once the STV and GM are calculated, five samples per year will be required to ensure compliance.

But is this frequency of sampling enough and are these E. coli limits suitable to reduce the number of outbreaks in leafy greens grown using untreated irrigation water? Should the mitigation strategy not have a greater focus on source water treatment and disinfection through a combination of filtration and UV or maybe chlorine dosing in minimal concentrations?

The International Ultraviolet Association (IUVA) will be conducting a webinar on January 15th to discuss some of these issues and possible mitigation strategies. To register before the webinar use the link below.


More information on the recent E. coli O157:H7 outbreaks can be found at the link below.