Summary

The Enteric Reference Laboratory (ERL) typed 697 STEC in 2023, a decrease of 84 from the prior year (613 in 2022). The most common serotypes of the 697 total isolates identified were O157:H7 (148, 21.2%) and O26:H11 (120, 17.2%) followed by O128:H2 (91,13.1%), O38:H26 (35, 5.0%), and O91:H14 (30, 4.3%). Although O157:H7 and O26:H11 remained the most common serotypes identified, the percentage of O157:H7 dropped from 34.1% in 2022 to 21.2% in 2023 while O26:H11 increased from 14.0% to 17.2%. Where subtyping of the stx gene was successful, 95/148 (64.2%) O157:H7 and 49/120 (40.8%) O26:H11 isolates were stx2a positive. This is a reduction from 2022 where 78.0% of O157:H7 and 55.7% of O26:H11 subtyped were positive for stx2a. The stx2a subtype was commonly detected in cases with haemolytic uremic syndrome (HUS) (11/13 cases, 84.6%) in New Zealand. Additionally, 12/13 cases with HUS with a typed isolate were either O157:H7 (1 stx2c and the rest stx2a) or O26:H11 (all stx2a) with the remaining case being an O104:H7 (stx1c present).