The number of Shiga toxin-producing E. coli (STEC) cases in Scotland decreased slightly in 2017 but remains high compared to other UK countries, according to Health Protection Scotland.

A total of 167 cases of E. coli O157 were reported to the agency compared to 181 in 2016. Non-O157 STEC declined from 63 in 2016 to 59 last year.

The Health Protection Scotland (HPS) surveillance report found E. coli O157 is the most commonly detected STEC serogroup and its potential to cause large outbreaks is exacerbated by its low infectious dose. Although large foodborne outbreaks have occurred in Scotland, sporadic infection predominates.

STEC can also be referred to as Verotoxigenic E. coli (VTEC) and Enterohaemorrhagic E. coli (EHEC).

HPS said reported rates of E. coli O157 infection in Scotland rose substantially in the mid-1990s and remain consistently high compared to other countries within the UK and Europe.

“Despite the variation in the number of cases seen annually, the consistently high rates of STEC infection reported in Scotland as compared to other UK countries, reinforces the need for the continued and comprehensive application of the wide range of existing control measures embedded in food safety and other guidance in Scotland,” added the agency.

A multi-agency group was set up to deliver recommendations in the VTEC Action Plan for Scotland and is due to report later this year.

Diagnostic laboratories investigate all diarrheal feces for the presence of E. coli O157 and refer isolates to the Scottish E. coli O157/STEC Reference Laboratory (SERL) for confirmation and typing. STEC of serogroup O157 is the only STEC for which routine standard tests are performed in diagnostic labs. Whole genome sequencing (WGS) typing was introduced at SERL in August 2017.

Orkney had the highest incidence rate of 13.7 per 100,000 while the Outer Hebrides (Western Isles) had a rate of zero per 100,000 with cases tending to peak in the summer months.

Children under 16 years of age accounted for 27 percent of cases and 18 percent of cases were older than 65 years old. As in previous years, children under five were the most affected with an overall rate of 7.1 per 100,000 people.

Phage type (PT) 21/28 and PT8 remained the two most frequently reported.

Non-O157 STEC

Lab and surveillance data is captured on non-O157 STEC, which account for about a third of all STEC infections in Scotland.

In 2017, 59 isolates of non-O157 STEC were cultured and reported by SERL to HPS. This compares to 63 isolates reported in 2016 and 78 in 2015. Last year, there were 25 reports of non-O157 STEC not confirmed by culture but were Shiga toxin positive. This was an increase from 19 in 2016. Overall, there were 78 reports of cases with non-O157 STEC in 2017.

Nineteen different non-O157 serogroups were identified in 2017, of which nine were only reported once. STEC O145 was the most common and accounted for 13 of non-O157 fecal culture positive cases. The next most common serogroups were O103 and O26, with 11 and eight reports respectively. It is the first year O26 was not the most common non-O157 STEC.

Information on hospitalization was available for 157 culture-confirmed cases of STEC. Of these, 36 percent were admitted to hospitals for at least one night during illness. That translates into 37 percent for O157 and 33 percent for non-O157.

During 2017, three general outbreaks of STEC were reported involving 13 cases. Three different serogroups were involved, O157, O145, and O26.

This is less than the number of outbreaks seen in past years with an average of five per year in the previous five years (2012-2016). In two outbreaks the main mode of transmission was considered to be foodborne, but a specific food vehicle was not identified and in the third, it was thought to contact with the environment.

Of the 157 cases for which HPS had information, 15 percent of all STEC cases were considered to have acquired their infection outside the UK.

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