A few of the patients said they had visited restaurants in France that share a common egg supplier, Spanish Packing Center A. The eggs came from three Spanish farms, and one egg sampled tested positive for the outbreak strain. Fresh table eggs from the supplier were withdrawn and redirected for use in heat-treated egg products. During summer 2021, no other countries received eggs from Spanish Packing Center A. As a result, the source of infection for cases in late 2021 and in countries other than France and Spain could not be established. 

Infections were noted in all age groups, from infants (less than 1 year old) to a 93-year-old patient. The two deaths included a 66-year-old French man and a 58-year old Spanish man. Out of the 60 cases where patients were interviewed, consumption of eggs in some form were reported, and 39 of 42 patients reported consuming poultry products.

Salmonella Enteritidis was also detected in a fecal sample from another Spanish farm's flock in September 2021. The farm is owned by and adjacent to the packing center. Spanish authorities observed that no own-check sampling had been executed at the farm as part of the National Salmonella Control Program since November 2019.