Source of rise in Swiss hepatitis E cases remains a mystery; pork investigated

Officials in Switzerland have been unable to find what was behind an increase in hepatitis E infections that affected more than 100 people in 2021.

The Federal Office of Public Health (FOPH) recorded a rise in cases of hepatitis E virus (HEV) between January and May 2021.

A total of 105 cases were reported across the country, which is almost triple the number compared to the same period in previous years. More men than women were affected and patients ranged in age from 18 to 87 years old. A total of 29 people were hospitalized with or following an HEV infection and two died.

Possible pork link
An investigation by FOPH, also known as OFSP, BAG and UFSP, included a case-control study and analyzing foodstuffs but no source could be identified.

However, the infections were shown to be caused by an HEV subtype which is found in pigs in Switzerland. More than half of cases were detected following blood donations and almost a third were asymptomatic.

Among patients, three clusters of linked cases were identified with 16 belonging to the first cluster, nine to the second and six to the third while 14 samples were not associated with any cluster.

From mid-April to late May, the Federal Food Safety and Veterinary Office (FSVO) tested meat products, in particular raw pork, raw pork liver and raw deer meat, for hepatitis E. From 198 samples, two pig livers and three sausages were positive. Sequencing virus isolates from food proved difficult but none of the pig liver positives matched those from human samples.

FSVO is looking at whether other measures or recommendations around the preparation and production of meat are necessary following the investigation.

Authorities advise that people with compromised immune systems or liver disease, the elderly, pregnant women and children should not eat raw or undercooked pork or wild boar meat products.

Symptoms of hepatitis E can include fatigue, poor appetite, stomach pain, nausea, and jaundice. However, many people, especially young children, have no symptoms. They usually appear from two to six weeks after exposure to the virus.

Hepatitis E model
Meanwhile, a model to predict thermal inactivation for HEV has been published by the Food Standards Agency (FSA).

Glasgow Caledonian University, Campden BRI, Jorvik Food Safety Services and the University of Strathclyde were part of the project.

Hepatitis E infection is an emerging issue in the UK and there is evidence to suggest an association with undercooked pork products. There is no standardized method for evaluating the stability of HEV that may be present in food during cooking processes or a suitable method to detect only intact HEV that can cause an infection.

Published evidence suggests heating does have an impact on HEV, but there is uncertainty on survival of the virus across a range of cooking times and temperatures and in different foods.

Minimum advice is to cook food to an internal temperature of 70 degrees C for two minutes. Data shows that HEV is more resistant than expected and that cooking at 70 degrees C to 75 degrees C (158 degrees F to 167 degrees F) may not fully eliminate the virus. However, it is unknown if it is still infectious.

The created model can help predict the amount of virus that will be degraded over a specific time and with cooking at a certain temperature. It can be adapted when advancements have been made in measuring HEV infectivity in food.

The model can be used to inform risk assessments, FSA advice to consumers and control measures in food safety management systems in industry.

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