The outbreak sickened 25 people with 19 developing haemolytic uremic syndrome (HUS) and three deaths.
The study provides data on the STEC O26 strains isolated from human cases of disease in Romania for first time and showed isolates belonged to a diverse population.
STEC O26 is considered emerging in Europe and in the last decade was the most frequent non-O157 STEC serogroup in human sporadic cases of infection including those developing HUS.
Romanian STEC O26 outbreak
In early 2016, Romania alerted the European Centre for Disease Prevention and Control (ECDC) of a rise in HUS cases in 15 children aged between five and 38 months.
Cases were linked to STEC O26 infection by serology and most lived in one of the southern districts.
An outbreak was suspected due to the high number of HUS cases in a short time (January and February 2016) among children from Arges district; this was a twofold increase compared with cases in the six previous years by four regional hospitals: Bucharest, Cluj, Iasi and Timisoara.
Food consumption history suggested dairy items from a local producer were potentially implicated as the source or vehicle of infection but this was not confirmed microbiologically.
Italy also had one HUS case with epidemiological link to Romania through the Early Warning and Response System (EWRS).
“The combined use of microbiological and serological techniques, the latter performed with ECDC support, brought evidence that STEC belonging to serogroup O26 were the cause of infection in most of the patients involved in the outbreak,” said the study.
“Before outbreak onset, difficulties in monitoring HUS across the country were due to the lack of mandatory reporting of HUS as well as the limited familiarity of many physicians with the clinical course of STEC infection and HUS owing to the rare occurrence of this condition.
“One of the strains, strain 2, was isolated from a child from Arges district with a history of exposure to the dairy products initially suspected to be implicated in the transmission of STEC O26 infection to the epidemic cases. The rest of the strains originated from children with no obvious exposure to such products.”
Characterisation of strains
The study included 15 STEC O26 strains isolated from cases with HUS (10), bloody diarrhoea (one) or non-bloody diarrhoea (four) across Romania between February and June 2016.
Strains were characterised by virulence markers (i.e. stx type/subtype, eae, ehxA genes), phylogroup, genetic relatedness and clonality using PCR-based assays, PFGE and multilocus sequence typing (MLST).
Virulence genes typing showed the strains from all the children with HUS carried the stx2a gene but STEC O26 strains harbouring only stx1 were found in children who did not progress to HUS. All STEC O26 strains possessed the intimin-coding gene eae.
PCR assays showed that 10 strains were positive for stx2 gene, either alone (five) or in combination with stx1 (five), while the remaining five were positive for stx1 gene alone.
Subtyping of the stx genes showed that the stx1-positive strains carried stx1a subtype and the stx2-positive strains harboured stx2a subtype.
The eae gene was found in all strains and ehxA in all but two of them. While eae and ehxA genes were detected irrespective of strain origin, a difference in distribution of the Shiga toxin-coding genes was observed.
Stx2 gene alone or associated with stx1 was found only in HUS-associated strains while stx1 as sole stx gene was only in strains recovered from children with diarrhoea.
The first six strains recovered during the outbreak were further characterised through WGS.
In silico WGS-based O and H serotyping assigned the six sequenced strains to the serotype O26:H11. WGS also confirmed that all these strains were members of ST21 clone.
“The 2016 outbreak clearly showed the need to rapidly detect and characterise the STEC strains causing human diseases with molecular typing techniques in order to understand their epidemiology and circulation, and thereby support targeted measures that limit human exposure to the source of infection,” said the researchers.
“As part of an effective strategy for the control of STEC infection in the population, the adoption of a sensitive national surveillance system for STEC infection and HUS is desirable. The system should be capable of providing data on the incidence of HUS and STEC infection at both the national and regional level, and describing the characteristics of both clinical cases and STEC strains.”
“Molecular characterisation of human Shiga toxin-producing Escherichia coli O26 strains: results of an outbreak investigation, Romania, February to August 2016”
Authors: Codruţa-Romaniţa Usein, Adriana Simona Ciontea, Cornelia Mãdãlina Militaru, Maria Condei, Sorin Dinu, Mihaela Oprea, Daniela Cristea, Valeria Michelacci, Gaia Scavia, Lavinia Cipriana Zota, Alina Zaharia, Stefano Morabito