STEC O26 infection was identified in 20 children with HUS in Italy in 2013 but no cases in adults were detected.
The case-control study showed an association between STEC O26 infection and dairy products from two local plants, but not specific ready-to-eat products.
E. coli O26:H11 strains lacking the stx genes were isolated from bulk milk and curd samples, but PFGE profiles did not match the outbreak isolates.
STEC O157 is the predominant cause of paediatric HUS worldwide but cases associated with infections with STEC belonging to non-O157 serogroups have been increasingly reported.
The researchers said STEC serotype O26:H11 seems to be evolving, with a shift from stx1 to the stx2 genotype in strains associated with past severe illness. This has public health relevance, since Stx2-producing E. coli O26 strains can cause a disease that is as severe as that caused by STEC O157.
Between 1 June and 30 September three years ago, 17 children with HUS in the Apulia region were admitted to the regional paediatric nephrology centre participating in the National HUS Registry.
The active case-finding revealed five additional children with HUS with a history of travel to the Apulia region: four were diagnosed in other Italian hospitals and one in a Swiss hospital.
Stool and serum samples from 19 HUS cases and serum only were found from the remaining three.
Stool examination yielded isolation of STEC O26:H11 strains positive for the stx2a and eae genes from seven cases.
STEC strains belonging to serotypes O80:H2, positive for stx2f and eae, and O non-typeable positive for stx2 group and eae were isolated from two other cases.
Four other cases had enrichment cultures positive for stx2 genes in PCR and/or had free faecal Stx.
Molecular typing of seven STEC O26:H11 isolates from cases showed two distinct STEC O26 strains were involved in the outbreak.
Evidence of infection with STEC O26 was obtained for 20 cases: 16 resident in the Apulia region and four travel-related. STEC O26 was isolated from five residents and two travel-related cases.
Potential link to dairy items
Dairy products of bovine origin consumed by 16 confirmed cases had been prepared by at least six different plants. These were inspected as well as 14 others supplying the retail outlets attended by the cases’ families.
“STEC O26 infection was significantly associated with the consumption of dairy products from two local plants and a drop in the occurrence of cases was observed after the adoption of control measures involving those plants.
“Neither the association of STEC O26 infection with specific products nor a laboratory evidence of STEC contamination in the final ready-to-eat dairy products could be demonstrated.”
The activity of one plant showed hygiene failures and was suspended. Pasteurisation of milk for dairy production was prescribed to three other plants.
A total of 218 samples of raw milk and dairy products of bovine origin were collected and tested for STEC. Sixty-five samples of fruit and vegetables, in particular watermelon, and five beef samples were also collected at retail and wholesale outlets identified through traceback investigations and tested. All the fruit, vegetable and beef samples were negative.
The enrichment cultures of 12 bulk milk or curd samples were positive for stx genes and, in 10 samples, for the eae and wzxO26 genes. E. coli O26:H11 strains lacking the stx genes but positive for the eae gene were isolated from two curd and two bulk milk specimens.
The researchers said the apparent absence of adult cases of infection could be explained by a lack of exposure to the source of infection.
Another possibility is the outbreak source was contaminated at a very low level, sufficient to cause disease in young children the most susceptible age group, they added.
“Community-wide outbreak of Haemolytic Uraemic Syndrome associated with Shiga Toxin 2-Producing Escherichia Coli O26:H11 in Southern Italy, summer 2013”
Authors: C Germinario, A Caprioli, M Giordano, M Chironna, MS Gallone, S Tafuri, F Minelli, A Maugliani, V Michelacci, L Santangelo, O Mongelli, C Montagna, G Scavia.