Spring onions from Egypt were likely behind a deadly E. coli outbreak in Denmark in 2021, according to researchers.

Between November and December 2021, the first recorded outbreak of enteroinvasive E. coli (EIEC) in Denmark occurred. A total of 88 sick people, including 58 women, with a median age of 52 and a range from 0 to 91 years old were detected. Three patients died.

only 34 patients were confirmed by culture, serotyping, and whole genome sequencing. Isolates from cases were grouped into two serotypes: 24 were O136:H7 and 10 were O96:H19. From 40 cases, the date of symptom onset ranged from mid-November to Dec. 24, 2021. The date of sampling was from Nov. 23 to early February 2022.

Sick people lived in four Danish regions. Symptoms included diarrhea and bloody diarrhea. Twenty-six people were hospitalized and three died within 30 days of testing positive for EIEC, according to a study published in Eurosurveillance.

Suspicion falls on imported spring onions

No related cases were reported from other European countries. However, in 2021, the UK had an outbreak of Shigella sonnei wher spring onions from the same producer in Egypt were the suspected source.

As it was the first EIEC outbreak in Denmark, there was no standard questionnaire available, so a trawling questionnaire usually used for Shiga toxin-producing E. coli (STEC) and Salmonella outbreaks were employed. Culture-independent diagnostic tests (CIDT) also made separating outbreak and sporadic cases difficult.

Interviews of 42 cases and traceback investigation pointed to ready-to-eat salads with fresh cabbage as the cause. In total, 27 of 42 cases reported having salad with fresh cabbage and 20 of them used the same grocery chain. While salads had different vegetables, imported spring onions were the only common ingredient. Environmental investigations failed to recover outbreak strains.

The Danish Veterinary and Food Administration (Fødevarestyrelsen) found that spring onions were imported pre-processed from the Netherlands and included by the Danish producer in the salads.

The agency examined samples of spring onions and ready-to-eat salads in December.  Shigella and EIEC were not detected. In November 2021, the Dutch supplier analyzed a batch of this product. The producer of ready-to-eat salads also examined samples of two batches of spring onions between late December and early January. No E. coli were detected in the tests. 

Spring onions originated from Egypt and were delivered by a Dutch business that rinsed and root-cut the product. No specific batches were identified as being the source of the outbreak.

Floods in Egypt

No recall occurred since the imported spring onions were part of ready-to-eat fresh salads, which had a short shelf life. The salad producer also changed the spring onion supplier.

The International Food Safety Authorities Network (INFOSAN) secretariat told Fødevarestyrelsen in late January 2022 that it had contacted the INFOSAN Emergency Contact Point in Egypt concerning the outbreak. However, the secretariat did not receive a response.

The Danish embassy in Egypt contacted Fødevarestyrelsen about the outbreak in February 2022, offering to assist. The embassy shared reports from 2021 indicating several instances of the Nile overflowing its banks. Flooding peaked with the onset of the rainy season in May 2021 and continued until December of that year.

“The outbreak underlines that high hygiene standards for imported fresh vegetables should be maintained when these are to be used in ready-to-eat products,” said researchers.