Application of multilocus variable number tandem repeat analysis to monitor Verocytotoxin-producing Escherichia coli O157 phage type 8 in England and Wales: Emergence of a profile associated with a national outbreak

Aims: Evaluation of multilocus variable number tandem repeat analysis (MLVA) to subtype all isolates of Vero cytotoxin-producing Escherichia coli O157 phage type 8 in England and Wales. Methods and Results: Over a 13 month period from December 2010, 483 isolates of VTEC O157 PT8 were tested by MLVA; 39% were received in the first 4 months of 2011, when infections are generally low. One profile, or single locus variants of it, was present in 249 (52%) isolates but was not common previously. These cases represented a national increase in PT8, associated epidemiologically with soil-contaminated vegetables. Most of the 177 other MLVA profiles were unique to a single isolate. Profiles shared by >1 isolate included cases from two small community, food-borne outbreaks and 11 households. Several shared profiles were found among 23 isolates without known links. Apart from one group, isolates linked to travel abroad had very diverse profiles. Conclusions: Multilocus variable number tandem repeat analysis discriminated apparent sporadic isolates of the same PT and assisted in detection of cases in an emerging national outbreak. Significance and Impact of the Study: Multilocus variable number tandem repeat analysis is an epidemiologically valid complement to surveillance and applicable as a rapid, practical test for large numbers of isolates.