A patient-control study in the Netherlands has identified traditional Dutch dry raw sausages as the main transmission route for hepatitis E virus to the general population.

Researchers said prevalence and cause of hepatitis E virus (HEV) contamination of pork muscle meat products requires further investigation. Traditional Dutch dry raw sausages of pork muscle meat, called “cervelaat,” “snijworst,” and “boerenmetworst” were reported by 72 percent of the patients, and 46 percent of controls. Direct contact with pigs and working with septic tanks are strong risk factors, according to the researchers.

A questionnaire on potential sources of HEV exposure, health, and socio-demographics was completed by 376 patients with acute hepatitis E, and 1,534 controls matched for age, gender and region of residence.

The nationwide case-control study was done between June 2015 and October 2017. Participants were asked about demographics, symptoms of illness, medical history, food consumption, foreign travel, and contact with farm animals, pets, pet food, and water.

The food assessment focused on a range of pork meat items, but also included beef products, game meat, organ meats of any animal, ready-to-eat products made with with meat, shellfish, unpasteurized milk, raw vegetables, soft fruits and berries, RTE salads and eating outside the home such as restaurants.

Cases were patients of all ages with a laboratory confirmed acute HEV infection. Most occurring symptoms reported by patients were fatigue, dark urine, nausea, stomach ache and headache.

Besides the three dry sausages of minced raw pork meat listed above, other ready-to-eat, but not all raw, pork products identified as risk factors included pre-packed liver sausage/pate, pork shoulder ham and smoked bacon. Among pork that requires cooking, “fresh pork sausage” of minced pork meat was identified as a risk factor. Pre-packed lettuce was the only risk factor for investigated fruits and vegetables.

Cases were more likely to usually buy meat at the supermarket. only nine reported they did not eat pork compared to 20 percent of controls.

Negative associations were observed for a few pork products. Pork butt (“procureurlapje”), cordon bleu, and chipolata sausage were associated with lower risk of acute hepatitis E. Compared to controls, cases also reported less consumption of steak (beef) and wild duck, and of forest fruits such as raspberries, blackberries, blueberries, red berries and blackcurrant.

Researchers said the identified host, food, and environmental risk factors for acute hepatitis E provides information for control, preventive strategies and advice to vulnerable high-risk groups.

“Assuming a causal relation, half (48 percent) of all hepatitis E cases would be prevented if the risk factors dry raw pork sausages such as “cervelaat”, “boerenmetworst” and “snijworst” would be eliminated,” they added.

To inactivate HEV, meat products should be heated to 70 degrees Celsius for at least 20 minutes.  However, dry raw pork sausages are generally consumed unheated and sliced on bread. Salting, fermentation and drying them largely inactivates pathogenic bacteria, but persistence of viable HEV after these processes is likely. However, further research is required to demonstrate dry raw pork sausages do contain infectious HEV.

In Mid-2017, the Dutch Meat Products Association advised members to stop using the diaphragm muscle of pigs in unheated products. A small decrease in HEV infected patients in the national lab surveillance system was seen in the second half of 2017. Pork diaphragm muscle is used as an ingredient in dry raw pork sausages, according to the association, and small amounts of pork liver often remain attached to it.

Researchers added comparison of risk factors and production methods between countries, considering international food trade, could strengthen understanding of transmission routes for HEV infection in Europe.