Investigation of a foodborne outbreak of Shigella sonnei in Ireland and Northern Ireland, December 2016: the benefits of cross-border collaboration and commercial sales data.

OBJECTIVES: To describe a cross-border foodborne outbreak of Shigella sonnei that occurred in Ireland and Northern Ireland (NI) in December 2016 whilst also highlighting the valuable roles of sales data and international collaboration in the investigation and control of this outbreak. STUDY DESIGN: A cross-border outbreak control team was established to investigate the outbreak. METHODS: Epidemiological, microbiological, and environmental investigations were undertaken. Traditional analytical epidemiological studies were not feasible in this investigation. The restaurant chain provided sales data, which allowed assessment of a possible increased risk of illness associated with exposure to a particular type of heated food product (product A). RESULTS: Confirmed cases demonstrated sole trimethoprim resistance: an atypical antibiogram for Shigella isolates in Ireland. Early communication and the sharing of information within the outbreak control team facilitated the early detection of the international dimension of this outbreak. A joint international alert using the European Centre for Disease Control's confidential Epidemic Intelligence Information System for Food- and Waterborne Diseases and Zoonoses (EPIS-FWD) did not reveal further cases outside of the island of Ireland. The outbreak investigation identified that nine of thirteen primary case individuals had consumed product A from one of multiple branches of a restaurant chain located throughout the island of Ireland. Product A was made specifically for this chain in a food production facility in NI. S. sonnei was not detected in food samples from the food production facility. Strong statistical associations were observed between visiting a branch of this restaurant chain between 5 and 9 December 2016 and eating product A and developing shigellosis. CONCLUSIONS: This outbreak investigation highlights the importance of international collaboration in the efficient identification of cross-border foodborne outbreaks and the value of using sales data as the analytical component of such studies.

Outbreak of hepatitis A infection associated with the consumption of frozen berries, Ireland, 2013--linked to an international outbreak.

In May 2013, a European alert was issued regarding a hepatitis A virus (HAV) outbreak in Italy. In June 2013, HAV subgenotype IA with an identical sequence was identified in Ireland in three cases who had not travelled to Italy. The investigation consisted of descriptive epidemiology, a case-control study, microbiological testing of human and food specimens, molecular typing of positive specimens and food traceback. We identified 21 outbreak cases (14 confirmed primary cases) with symptom onset between 31 January and 11 October 2013. For the case-control study, we recruited 11 confirmed primary cases and 42 matched controls. Cases were more likely than controls to have eaten berry cheesecake (matched odds ratio (mOR): 12; 95% confidence interval (CI): 1.3-114), whole frozen berries (mOR: 9.5; 95% CI: 1.0-89), yoghurt containing frozen berries (mOR: 6.6, 95% CI: 1.2-37) or raw celery (mOR: 4; 95% CI: 1.2-16). Among cases, 91% had consumed at least one of four products containing frozen berries (mOR: 12; 95% CI: 1.5-94). Sixteen food samples tested were all negative for HAV. As products containing frozen berries were implicated in the outbreak, the public were advised to heat-treat frozen berries before consumption.