Yersiniosis outbreaks in Gold Coast residential aged care facilities linked to nutritionally-supplemented milkshakes, January–April 2023

In January 2023, an outbreak of <i>Yersinia enterocolitica</i> in residential aged care facilities (RACF) was identified by the Gold Coast Public Health Unit and confirmed using whole genome sequencing. During the outbreak period there were 11 confirmed and 14 probable cases of <i>Y. enterocolitica</i> notified in RACF and 30 suspected cases with compatible illness. Eleven cases (20%) were confirmed as Biotype 1A non-typable (BT1A NT) sequence type (ST) 278 within 4-15 single nucleotide polymorphisms (SNP) of each other. Combined epidemiological, trace-back and laboratory investigations identified nutritional milkshakes, stored at ideal growing conditions for <i>Yersinia</i> and given to vulnerable RACF residents, as the likely outbreak vehicle. This highlights that <i>Y. enterocolitica</i> Biotype 1A can be pathogenic in humans and transmission via atypical sources should be considered in outbreak investigations. This report outlines the response and challenges associated with investigating outbreaks in aged care.