A Listeria outbreak in Spain that sickened more than 200 people in 2019 and killed three was caused by stuffed pork, according to a recently published study.

It was the largest listeriosis outbreak in Spain and one of the biggest in Europe. based on hospitalization records, Spain has seen a rising trend in such infections since 1997, reported the study published in the journal Eurosurveillance.

Between July and October 2019 in Andalusia, an outbreak with 207 cases of listeriosis was identified. Confirmed cases had a median age of 44 with a range of 0 to 94 years old and 114 were women.

Four provinces were affected with 163 confirmed patients in Seville, 29 in Huelva, 11 in Cadiz and four in Malaga. In Andalusia, stuffed pork is popular, as it is a low-cost, traditional ready-to-eat (RTE) food. It consists of a cold cut of roasted pork with garlic, spices, and salt.

Patient details
Most sick people had mild gastroenteritis, 141 required hospitalization and three died; five of 34 pregnant women had a miscarriage. The three patients who died were above the age of 70. The median incubation period was one day with a peak of 43 patients notified on a single day in mid-August.

Stuffed pork, an RTE product consumed unheated and contaminated with Listeria monocytogenes sequence type 388 was identified as the source of infection. The “La Mecha” brand chilled pork was produced by Magrudis. Most cases reported having purchased the stuffed pork at a variety of establishments but primarily supermarkets and bars.

Facua, a consumer group, is representing about 80 sick people, as part of a civil action. A criminal trial is ongoing with certain staff at the company facing up to 10 years in prison and a local veterinarian who carried out inspections at Magrudis also facing charges.

Active case finding identified 16 additional WGS-confirmed patients before the outbreak started by several months with illness onset dates from November 2018 to June 2019. Epidemiological interviews revealed only one sick person had contaminated meat. So, they have deemed historically associated cases and are not included in the outbreak investigation.

An additional 11 outbreak cases came from six different regions in Spain. French authorities notified a confirmed case of an individual who had consumed pork meat in Seville in mid-August. A link to several cases of listeriosis in Germany could not be established by public health authorities.

Investigations by authorities
The outbreak strain was identified in 189 human samples, 82 food, and five environmental samples.

The first inspection at the Magrudis plant in mid-August 2019 found no positive samples. However, there were four contaminated food and five environmental samples were identified within the first 10 days. During the next two months, 55 additional food samples from the factory were found to be contaminated. Most were taken between mid and the end of August.

Listeria monocytogenes was quantified in 42 food samples with values well above the limit set by European unio regulations of 100 colony-forming units per gram (CFU/g).

A public health alert was announced in mid-August 2019. The next day, cleaning and disinfection of the Magrudis plant were done and stuffed pork from the site was recalled. A few days later, production was stopped and the recall expanded to any meat produced in the facility before it was extended again to include every food product. The recall was estimated to include more than 8 tons of meat products.

By the end of the outbreak, Listeria monocytogenes were detected in 87 samples. Most positives came from products involving stuffed pork and other pork items.

The remaining five samples were environmental, mostly from machinery surfaces. These included an oven trolley, meat injectors, which are metal syringes used to add condiments to meat, and an air conditioner vent. Eight food samples were shown to harbor the outbreak strain by WGS.

Poor hygiene conditions at the site could explain the contamination of meat products, which might have happened after thermal treatment and before delivery to grocers or sellers. There is also a need to improve food distribution records. Identification of all the establishments to which the stuffed pork had been sent was not as fast as desired, said researchers.