Researchers have estimated that around 7,500 Yersinia enterocolitica infections may go undiagnosed in England annually.

Findings suggest a considerable number of yersiniosis cases are not recorded. The apparently low amount is probably due to a lack of laboratory testing, said experts.

Scientists examined data on Yersinia cases in England between 1975 and 2020 to describe trends over time and to estimate the current number of undiagnosed Yersinia enterocolitica cases. Results were published in the journal Eurosurveillance.

Yersiniosis is one of the most common bacterial foodborne agents in Europe. There is a large variation among countries, with the highest rates in Denmark and Finland and the lowest in Romania and Bulgaria. The reported incidence in the United Kingdom is well below the European average.

UK standards state that fecal specimens should only be tested for Yersinia species with a clinical suspicion of yersiniosis.

Impact of one lab
Overall, 8,023 laboratory-confirmed Yersinia infections were recorded in England between 1975 and 2020. Cases increased sharply during the 1980s to a peak in 1988 and 1989, followed by a steep decrease. Incidence remained low until 2016. The majority of infections from 1975 to 2020 were caused by Yersinia enterocolitica.

From 2017 to 2020, an increased incidence was observed in association with one laboratory in Portsmouth in the South East of England implementing routine PCR testing.

Yersinia enterocolitica cases reported by the Portsmouth lab accounted for almost 60 percent of 546 patients reported in England. The average annual incidence of infections for the catchment population of the lab was 13.6 cases per 100,000 population.

If this incidence was consistent across England in the catchment populations of labs not undertaking routine PCR testing, an average of 7,500 Yersinia enterocolitica infections were undiagnosed annually from 2017 to 2020, said researchers.

“Our study suggests that the true incidence of Yersinia enterocolitica infections in England may be as high as, or higher than in other parts of Europe, the historical decline was artefactual, and that we may lack good data to identify the true trend over time,” they added.

Infection Sources and patient impact
Scientists said changes to the epidemiology of Yersinia infection had gone unnoticed and may reflect changing sources of infection.

There was a decrease in the proportion of young children sick and an increase in cases affecting people aged 65 and older. Almost one-third of all cases in England from 2017 to 2020 were diagnosed in May and June, while no such seasonal pattern was seen in earlier data.

Surveillance questionnaires were completed by 45 of 115 patients covered by the Portsmouth lab between 2018 and 2019. Common symptoms were diarrhea, stomach pain, nausea, and headache. Also reported were joint/back pain, vomiting, fever, muscle pain, blood in stool, and dizziness/fainting.

Questionnaire completion was a median of 29 days after the symptom onset date was reported. Around half of respondents said they were still ill at this time. For those who had recovered, the median duration of illness was 16 days. wher data was known, nine of 44 had been admitted to the hospital for a median of two days.

Results suggest that yersiniosis may present a considerable burden to patients, with most having ongoing symptoms two weeks after disease onset.

Eighteen people had treatment for illness with antibiotics. Travel or return to the UK from abroad within seven days before the illness was reported by 10 people. No contact with pigs was mentioned but six people said they had handled raw pork or gammon in the week before illness.

Researchers said findings provide a compelling argument for an approach to Yersinia surveillance in England and other countries that includes routine testing and follow-up of cases by epidemiological questionnaire.