Yersiniosis is a gastrointestinal infectious caused mainly by the bacteria Yersinia enterocolitica (YE). In New Zealand (NZ), there were 1,294 notified cases in 2022, which at a rate of 25.3 cases per 100,000 population is at least 10-fold higher than other industrialised countries.
We report a case-control study involving notified human cases of yersinosis cases within two NZ regions, as well as whole genome sequencing (WGS) analysis of YE obtained from clinical cases and from source testing.
Of the 291 notified yersiniosis cases reported within the study period, 247 cases were interviewed and consented to participating in the case-control study completing telephone questionnaires of potential exposures and disease burden. Pathogenic YE bioserotype 2/3, O:9, corresponding to sequence type (ST) 12 (McNally scheme) predominates in NZ, with 46% of consenting cases confirmed with this type. Pathogenic YE bioserotype 2/3, O:5, 27, and 4, O:3 (corresponding to ST14 and ST18, respectively) were also observed in 5% and 3% of consenting cases, respectively. Exposure to pork was identified as a significant risk factor for pathogenic YE and source testing (n = 499) confirmed the presence of pathogenic YE in 15% of retail raw meat, primarily raw pork. The use of WGS analysis confirmed multiple genetically very closely related clusters of pathogenic YE, predominately from raw pork with clinical cases from both NZ regions.
The pathogenicity of YE Biotype (BT) 1A remains controversial internationally but this BT is notifiable in NZ and was observed within 27% of consenting cases. A diverse range of STs were observed within the YE BT 1A isolates obtained from both clinical and food samples. Risk factors associated with YE BT 1A included the consumption of cooked seafood, sushi, tofu and some vegetable types.
Examination of demographic data of participants, and notified cases from across New Zealand identified significant differences in distribution of biotypes across New Zealand, and of the ethnicity and age groups affected by biotypes.
This study demonstrates the power of combining the analysis of specific risk factors and WGS to indicate that raw pork is a significant risk factor for yersinosis attributed to pathogenic YE bioserotypes but not for YE BT 1A. This study has generated up-to-date evidence on potential sources of YE in NZ and will help devise control strategies to improve the yersinosis public health outcomes.