Dutch 2023 illness data reveals large Salmonella outbreak

According to a recent report, reports of most foodborne pathogens increased in the Netherlands in 2023 compared to the year before, and a large Salmonella outbreak with 150 cases was recorded.

According to the National Institute for Public Health and the Environment (RIVM), the number of people with gastrointestinal illnesses in 2023 was comparable to before the COVID-19 pandemic. However, there were a high number of infections with Shigella, Shiga toxin-producing E. coli (STEC), norovirus, Cryptosporidium, and leptospirosis.

Investigations were conducted into an outbreak of campylobacteriosis, four salmonellosis outbreaks, and an STEC outbreak. The source of two salmonellosis outbreaks was eggs from laying hen farms and dry sausage that had insufficiently matured. Data comes from the annual report on enteric, vector-borne, and zoonotic infections.

A total of 4,672 campylobacteriosis patients were registered, which is slightly lower than the 2022 figures. Of the 475 Campylobacter isolates sent to RIVM and typed using Whole Genome Sequencing (WGS), 189 belonged to a cluster, and 57 clusters were detected with two to 15 isolates.

A patient survey in an outbreak with 15 cases did not reveal a source. However, when sharing sequence data with other countries via the European Centre for Disease Prevention and Control (ECDC), two food isolates from Danish surveillance were found to cluster with several patients from Denmark. The food isolates came from poultry meat from Poland and Lithuania. Danish officials informed the relevant authorities, focusing on the trade of chickens between countries.

Salmonella situation
The number of estimated salmonellosis cases was 2,368. Infections were highest among children aged 1 to 4 and 15 to 34.

The percentage of travel-related cases was higher than before the pandemic. However, the share of travel-related Salmonella Enteritidis cases was much lower than pre-pandemic. Overall, there was an increase in Enteritidis cases and a decrease in Typhimurium and monophasic Typhimurium.

All Salmonella isolates sent to RIVM were typed using WGS. Ninety-three clusters of Salmonella Enteritidis, 59 of Salmonella Typhimurium, and 118 clusters of other serotypes were detected. The Salmonella Enteritidis clusters ranged from 2 to 194 isolates.

A Salmonella Enteritidis outbreak affected 156 people including 76 men and 80 women. Patients had a median age of over 41 and ranged from 1 to 98 years old. The Dutch Food and Consumer Product Safety Authority (NVWA) and COKZ, the Dutch supervisory authority for dairy, poultry, and eggs, revealed transmission via contaminated eggshells to animal feed. A link to laying hen farms was found, which could explain human cases.

A monophasic Salmonella Typhimurium outbreak was traced to dry sausage. It involved 16 patients from the northeast of the country. Seven were women, and nine were men, with an average age of 18. Reports from the company showed that the maturing time was not long enough to eliminate Salmonella.

A Salmonella Infantis outbreak sickened seven women and three men, with patients either under 30 or over 80 years old. One older person died, but the outbreak ended with no source found. 

E. coli and Listeria figures
A total of 576 people had an STEC infection in 2023, down slightly from the previous year. 2022 had seen the highest total since 2016.

From patient isolates received by RIVM, the most common serotypes were O157 and O26. A total of 34 different serotypes were found. Twenty-one patients developed hemolytic uremic syndrome (HUS), including three with STEC O157 and two with STEC O26. Nine were children aged under 1 to 12 and the other patients were aged 49 to 77.

Five people died directly or indirectly after STEC infection. The three with HUS were one child and two adults over 55 years old, while two people older than 70 did not have HUS. Of the 550 patients with information, almost a quarter were infected abroad. The most frequently mentioned countries were Egypt, Turkey, and Indonesia.

One outbreak with 15 cases was identified. Patients ranged in age from 2 to 61. No source was found, but epidemiological data highlighted that sick people often ate raw vegetables at fast-food restaurants. Another 20 clusters were identified.

For Listeriosis, 95 patients were reported, and 14 people aged 57 to 87 died directly or indirectly after infection. The median age of all cases was over 69 and ranged from 23 to 93 years old.

WGS identified 19 clusters with one or more isolates from 2023. Some clusters included isolates from several years. Four clusters were related to persistent contamination at meat and fish processing locations.

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