The number of people infected by Shiga toxin-producing E. coli nearly doubled in Denmark from 2014 to 2018.

There were 281 cases in 2014 and 495 in 2018. The largest increase was from 2017 to 2018 and highest incidence was in East and West Jutland. A high number of Shiga toxin-producing E. coli (STEC) infections were seen in the summer from June to September. The most common types of E. coli were O157, O26, O103 and O146.

Statens Serum Institute (SSI) figures show the number of bacterial intestinal infections due to STEC followed an increasing trend in the period.

“Part of the explanation may be that the diagnostic methods and clinical criteria for STEC testing have changed at several departments of microbiology in the 2014-2018 period. Thus, more people are tested and diagnosed than previously,” according to the agency.

Demographics of those infected
In Denmark, STEC infections are monitored at SSI via two systems. In these, 1,609 cases were reported in the period. Eleven people had the same STEC type for more than six months and eight had more than one STEC type verified.

In total 63 percent, or 1,033 of all STEC patients, were registered as having become infected in Denmark. Place of infection was unknown for 18 percent while 19 percent were infected abroad, primarily in Europe, the Middle East and Africa.

The median age of those infected was 23 years, and a third of the patients were children younger than 8 years old. Females accounted for between 53 percent and 58 percent of annual cases.

HUS and outbreaks
From 2014 to 2018, 55 hemolytic uremic syndrome (HUS) infections, or 3.4 percent of all STEC patients, were recorded. More HUS cases were reported in the older than 7 years old age group and an increase was observed in 2018.

The median age of HUS cases was 6 years and 50 percent were between 2 and a half and 13 years old, with an overall age range of 0 to 80 years. This past year saw 21 HUS patients, which is the highest annual number to date. It is too early to say if the rise in 2018 forms part of a larger annual trend, according to SSI.

STEC isolates have been whole genome sequenced at SSI since 2014. During 2014 to 2018, 55 clusters were found, counting two or more people with genetically related types. A total of 45 of these included two to four patients and eight clusters comprised five to eight patients. In six genetically related clusters infection from foods could have occurred.

The 2016 to 2018 period had a larger cluster of 15 genetically related cases and an O26:H11 outbreak in 2018 with 38 patients.

The largest outbreak in Denmark was recorded in 2018 with 38 cases. Cases in the E. coli O26 outbreak primarily occurred among children younger then 4 years of age. It was likely associated with eating beef salami, but the bacterium was not detected in samples of the product.

Another outbreak in the same year saw seven cases of O111:H8. One confirmed and two probable cases developed HUS. Cases were scattered across Denmark and none had travelled abroad during the incubation period. No common source could be established but minced beef was an unconfirmed suspicion as this was the only food that all patients said they had eaten.