Several people part of a Salmonella outbreak in Denmark tasted or ate raw or undercooked sausage, according to a recently published study.

In November 2018, an outbreak of monophasic Salmonella Typhimurium was detected. It sickened at least 49 people across the country.

A traditional form of raw Danish pork sausage called medister sausage was believed to be the source of illnesses. Product samples were negative for Salmonella and investigations at the production site did not reveal the source of contamination. Medister sausage is often served in the late autumn months and Christmas season. It is a long, thick sausage made from ground pork, seasoned and stuffed into casings.

Due to a control program, Salmonella Enteritidis is all but eliminated in Danish broiler poultry and egg production but Salmonella Typhimurium still exists in pigs and pork.

Risky behavior
In mid-November 2018, Statens Serum Institut (SSI) noted eight cases of monophasic Salmonella Typhimurium belonging to the same WGS cluster. The sequence type (ST) 5296 had not been detected before but was closely related to ST 34 which is often found in pork products.

In eight initial hypothesis generating interviews, seven people said they had eaten a certain type of classic Danish raw pork sausage known as medister sausage, according to a study published in the journal Epidemiology and Infection.

The median age was 65 years with a range from 11 months to 97 years and 53 percent were male. Seven of 49 cases were children less than 18 years of age.

Thirty people were hospitalized and 13 reported bloody diarrhea as one of the symptoms. There were no deaths. The onset date of illness was known for 38 of 49 patients and was between Oct. 14, 2018, and Jan. 17, 2019.

Almost all interviewed patients had eaten fresh pork and 28 of them ate medister sausage in the week prior to becoming ill with Salmonella.

Six patients said they had partly eaten the medister sausage raw or undercooked. Five people said they had failed to boil it prior to frying as is normally recommended on packages and by the Danish Veterinary and Food Administration (DVFA). In one family a child had eaten medister sausage that was not thoroughly cooked.

“Consumers have to make sure that pork is handled correctly, in particular when it comes to raw products that need to be thoroughly cooked before consumption. Tasting raw meat or eating undercooked pork meat should be discouraged,” said researchers.

Attempted trace-back findings
Traceback investigations pointed to one manufacturer of minced meat and prepared meat products. A total of 90 batches of ground meat and of prepared meat, including nine batches of medister sausage, were analyzed for Salmonella. only one sample from a batch of minced pork patty sampled in January 2019 found Salmonella but it was not related to the outbreak strain. Medister sausages were packed at the production site and no handling of the sausage took place at supermarket level.

“No breaches in procedures or obvious incidents that could explain the presence of a specific type of Salmonella in multiple batches of medister sausage in a prolonged period of several weeks were identified,” according to researchers.

The DVFA also investigated results of routine sampling at the slaughterhouse providing meat to the manufacturer. As part of mandatory sampling, one of every 1,000 carcasses were swap sampled and analyzed for Salmonella. It was detected eight times in these samples, but none were identical to the outbreak strain.

Because shelf life of medister sausage is short and fresh meat is used for production, none of the raw material meat used to produce the batches suspected of having caused illness was available from the manufacturer by the time the outbreak was detected and investigation started.

Researchers said it was likely the bacteria might be present in low numbers and unevenly distributed in the raw material so the chance of detecting it at sampling might be limited. High fat content may also increase thermal resistance of bacteria so it is not fully eliminated by heating.

“It is also likely that only a low Salmonella dose is sufficient for patients to become ill as medister sausage is a product with a high content of fat (10 to 20 percent) that protects the bacteria past the barrier of the gastric acid.”

Samples of medister sausage from more manufacturers, as part of routine surveillance and companies own checks, were positive for Salmonella during the outbreak period. This includes finding the serovars Mbandaka, Typhimurium and its monophasic variant, which was different from the outbreak strain.