Children up to four years old accounted for almost one-third of confirmed Shiga toxin-producing E. coli (STEC) cases in 2017, according to the European Centre for Disease Prevention and Control (ECDC).

A total of 6,647 infections with STEC, also known as verocytotoxin-producing E. coli (VTEC), were reported by 30 European countries and 6,457 were confirmed making it the fourth most common zoonosis in the EU.

The highest rate of confirmed cases was in the age group 0 to 4 years (8.9 cases per 100,000 population). This notification rate was four to nine times higher than older age groups, as it was for 2016 figures.

Hemolytic-uremic syndrome (HUS) mainly affects small children and is characterized by acute kidney failure requiring hospital care. Two-thirds of HUS cases were in patients up to 4 years old.

The number of confirmed STEC cases remained stable between 2013 and 2017 but at a higher level than when surveillance started in 2007 and before a large outbreak in 2011.

“Part of the increase may be explained by improved clinical awareness of STEC/VTEC infection following the 2011 outbreak. Other contributing factors could be the increasing number of laboratories that were testing for serogroups other than O157 and shift in diagnostic methods from culture to culture-independent methods, with PCR more commonly used,” according to ECDC.

Highest notification rate in Ireland

The highest number of confirmed cases was reported by Germany (2,065) and the United Kingdom (993), both of which accounted for 47.4 percent of all infections. The same two countries reported the most cases in 2016 and 2015.

As in previous years, the highest country-specific notification rates were in Ireland (795 cases), Norway (381), Sweden (504) and Denmark (263), with 16.6, 7.2, 5 and 4.6 cases per 100,000 population respectively. Bulgaria, Cyprus, and Lithuania recorded no cases in 2017.

On average, 37.5 percent of STEC cases with known information were hospitalized and 20 died. The average proportion of hospitalized cases increased compared to previous years.

Serogroup O157 was most commonly reported, but the proportion continued to decrease, while the number of non-O157 STEC serogroups increased. The top six non-O157 serogroups were O26, O103, O91, O145, O146, and O111, which have steadily increased in the EU since 2007 in human and food samples.

Non-O157 accounted for more HUS cases than serogroup O157, emphasizing an emerging risk of severe infections and the potential for large outbreaks, according to ECDC.

Outbreaks linked to meat and dairy

Most STEC cases (83.5 percent) with information on the country of infection were domestically acquired. Of the confirmed cases with known gender 55 percent were female.

A clear seasonal trend was observed between 2013 and 2017, with more cases reported during the summer months from June to September.

In 2017, 48 STEC outbreaks were reported to the European Food Safety Authority (EFSA) involving 260 cases in 11 countries and accounting for 0.9 percent of all food- and waterborne outbreaks at EU level.

Nine of the 37 foodborne outbreaks were reported with known food vehicle. Four were caused by bovine meat and products thereof (STEC O157), one by meat and meat products (STEC unspecified), three by milk (STEC O157 and STEC unspecified) and one by cheese (STEC O111).

In Ireland, wher the highest country-specific notification rate in the EU was reported, STEC was the most frequently reported causative agent and was identified in 50 percent of outbreaks in 2017, including 11 waterborne incidents.