Hard-to-identify E coli strain found in UK outbreak

Jun 8, 2006 (CIDRAP News) An unusual strain of Escherichia coli O157 that standard laboratory culture methods cannot detect has been identified in a disease outbreak associated with a nursery in Scotland and in other cases in Scotland and England, according to recent news reports.

The outbreak strain grows on sorbitol-containing agar (SMAC) and does not grow on the selective media (CT-SMAC) usually used for Shiga toxinproducing E coli (STEC) O157. Thus, illness cases caused by this strain, called a sorbitol-fermenting strain, could be missed in laboratories unless other testing methods are used.

The disease outbreak began at a nursery in Dunfermline, Scotland, on May 9, and had involved 13 cases of gastrointestinal illness in children and adults by late May, according to BBC News reports. Four children were hospitalized for treatment for hemolytic uremic syndrome (HUS), physicians at the Royal Hospital for Sick Children in Glasgow told BBC News.

Health Protection Scotland stated that the sorbitol-fermenting strain has been rare in the United Kingdom, the BBC reported. The strain had first been identified in Germany in 1988 and was thought to be restricted to continental Europe until 2002, when it was identified in Australia and the UK.

Four unrelated adult cases of infection with the same strain have been identified elsewhere in Scotland, as have four cases in Yorkshire and the Humber region in England, according to BBC News reports.

The cases in England occurred about the same time as the Scottish nursery outbreak. The English samples were received for testing between April 25 and May 4 in conjunction with cases of HUS. Typing showed the isolates to be the same, and the BBC reported that investigators from Scotland and England were working together to determine whether any common factors link the cases from the different regions.

UK health authorities have issued revised guidelines to laboratories and specialists to address possible cases involving this strain, according to a report in the May 25 Communicable Disease Report Weekly, published by the UK Health Protection Agency. They recommend that when clinical symptoms suggest STEC, especially in children younger than 15 years and adults 65 or older, and presumptive sorbitol-nonfermenting E coli O157 colonies are not observed on SMAC or CT-SMAC, then sorbitol-fermenting colonies should be tested for agglutination with E coli O157 antiserum. Colonies that have positive agglutination tests should be identified as E coli and sent to the proper health laboratory for confirmation, phage typing, and detection of Shiga toxin genes.

Dr John Cowden, a Health Protection Scotland consultant, said clinicians had been urged to ensure that this unusual strain of E coli was not missed when screening samples from patients suspected of having any type of E coli O157 infection.

In a BBC story, Dr Cowden said, "This unusual strain reacts differently in the laboratory from other types of E coli O157, and this is why we are interested in finding out more about it. It produces the same symptoms as other strains, and our advice to reduce the possibility of becoming infected with any type of E coli remains the same."