Scientists have studied E. coli cases in Ireland to try and gain new insights into factors associated with serious infections.

Shiga toxin-producing E. coli (STEC) infection can cause potentially fatal hemolytic uremic syndrome (HUS).

Researchers conducted a case-control study with 108 HUS patients and 416 unmatched non-HUS controls seleced among STEC notifications in Ireland during 2017 to 2020. 

Findings published in the journal Emerging Infectious Diseases reaffirmed known risk factors, such as young age and presence of specific Shiga toxin (stx) genes or gene combinations.

They also suggested that having an outbreak-associated infection, living in the East region of Ireland, and the presence of certain genes are potentially associated with developing HUS. 

“The higher odds of HUS among patients residing in the East of Ireland, likely representing a more urban environment, might be because patients in more rural environments are protected by repeated previous STEC exposures, although we cannot confirm that hypothesis. Another possible reason is the higher density of childcare facilities in the East region; children are more likely to be associated with an STEC outbreak in a childcare setting in the East and therefore may have a higher risk for HUS,” said scientists.

Irish STEC burden
STEC is a major public health problem in Ireland. The country has reported the highest incidence rate among European unio member states for many years. In 2017, 27 STEC cases in Ireland led to HUS.

The number of isolates by year increased from 99 in 2017 to 154 in 2018, decreased to 135 in 2019, and increased again to 141 in 2020.

Among 524 patients, 233 were up to 9 years old and 291 were above the age of 10. A total of 53 percent were female and 47 percent male. The highest proportion of patients was in the South with 104 followed by the Southeast and East both with 82. Ninety-three patients had outbreak-associated infections.

Isolates from 187 patients were serogroup O26, and isolates from 122 patients were O157. Other notable serogroups were O145, O103, O111, and O55.

The stx subtypes most commonly found in patients’ isolates were stx2a alone, stx1a alone, or both stx1a and stx2a.

Patients up to the age of 9 had 3-fold odds of HUS compared with those older than 10. Those with outbreak-associated infection had above 3-fold odds of HUS compared with cases whose infection was not outbreak-associated.

Compared with patients who had stx1a alone, the odds of HUS were higher among patients with stx2a alone, both stx1a and stx2a, or both stx1a and stx2c.

The presence of eae genes, described elsewher as being connected with HUS, was not significantly associated with the condition in the current study.

“Our findings, particularly if validated by further studies, could improve early identification of higher-risk STEC infection and help guide enhanced surveillance and public health management,” said scientists.