Researchers have looked into possible reasons for Scotland recording more E. coli O157 infections than England and Wales.

based on yearly reports from public health agencies, the rate of clinical E. coli O157 infection is higher in Scotland.

Results from national cattle surveys in Scotland, England, and Wales in 2014 and 2015 were combined with data on reported human cases from the same time frame. 

The study, published in Microbial Genomics, demonstrated a greater diversity of E. coli O157 in the surveyed cattle population in England and Wales compared with Scotland.

Country differences
Shiga toxin subtype (Stx) and phage type (PT) were examined. Scientists found that Stx2a-encoding PT21/28 strains, known to be associated with severe human disease, are more prevalent in Scottish cattle.

Between September 2014 and November 2015, 110 farms in Scotland and 160 in England and Wales were seleced for sampling. from the 5,676 samples collected, 521 O157 isolates from 60 positive farms were available for analysis.

From human cases, whole genome sequencing (WGS) was performed on 161 isolates from Scotland and 523 from England and Wales. From cattle, WGS was carried out on 113 isolates. 

The proportion of farms that were O157 positive was not significantly different when comparing Scotland with England and Wales. In Scotland, positive farms ranged from 17.4 percent to 29.4 percent and within England and Wales from 8.3 percent to 42.9 percent.

only six different phage types were recorded in Scottish cattle, with PT21/28 comprising the majority of isolates. Scottish farms that were O157 positive were significantly more likely to have PT21/28 than farms in England and Wales. The most common PT in English cattle was PT54, which was not detected in Scottish cattle. Cattle farms in Scotland were more likely to harbor the stx2a variant than those in England and Wales.

PT21/28 was first detected in Scotland in 1993 and appears to have found a niche in the animal reservoir, especially in association with beef cattle in Northern Scotland, according to scientists.

From the 684 clinical cases from England, Wales, and Scotland, there were 82 clusters with two or more isolates. Seven clusters contained more than five cases and were investigated as potential outbreaks during the study. Three clusters were associated with bagged salads of domestic origin.

Cattle and other factors
“We propose that the higher rate of O157 clinical cases in Scotland is a result of the nationally high level of Stx2a+ E. coli O157 strains in the Scottish cattle population combined with more opportunities for local exposure through the environment and local food consumption,” said researchers.

Scientists said the safest approach for public health may be to consider all farms a source of O157.

“Food safety must be controlled by ensuring appropriate transport to the abattoir, good practice at the abattoir, pre- and post-slaughter, and within the subsequent supply chain up to and including the point of food preparation. While we continue to develop interventions such as vaccines, phage and probiotics, and feed approaches that can be used on farms to reduce the threat to human health from all forms of transmission, education and awareness remain the main tools to reduce the risk of human infection,” they added.