The source of infection was not found for three of four Listeria outbreaks in England in 2018.
The one which was solved was an international outbreak that involved 12 cases in England from 2015 to 2018 and was traced to frozen sweetcorn and vegetables produced by Greenyard in Hungary.
The company found the cause of contamination, a persistent presence of Listeria monocytogenes in one of the freezing tunnels, and closed down this tunnel at the plant. In June 2019, the factory was sold to Roger & Roger, a producer of potato and corn snacks.
This multi-country incident included 54 clinical cases of listeriosis in Australia, Finland, Sweden, Denmark, Austria, and the UK with 10 deaths. The outbreak was detected in Finland using whole-genome sequencing (WGS).
Traceability information indicated that frozen corn was produced in Hungary and packed in Poland. It was found that people had eaten the frozen sweetcorn uncooked, although instructions on the packaging told consumers to cook it. Implicated frozen products were distributed to 116 countries.
The second incident involved four people with illness onset in 2017 and 2018. The third outbreak sickened three people and the final one had five reported cases all in 2018.