Major listeriosis outbreak in Spain caused by contaminated stuffed pork

Major listeriosis outbreak in Spain caused by contaminated stuffed pork

Listeria bacteria are ubiquitous in the environment, and consumption of foods contaminated with Listeria monocytogenes is one of the main routes for foodborne outbreaks. Healthy adults may not even develop symptoms after eating contaminated food. However, listeriosis can cause serious health problems in pregnant women, newborns and people with weakened immune systems. The incidence of listeriosis has been increasing steadily in Europe since 2008, with an upward trend observed in Spain since 1997.

Between July and the end of October 2019, contaminated food caused a major outbreak in the southern Spanish region of Andalusia, with 207 confirmed cases. In their outbreak report, Fernández-Martínez et al. Describe the investigations carried out to determine the cause of the infections and the reasons for the rapid spread of the infections (the mean incubation period was 1 day) -; with a peak of 43 symptomatic patients reported on one day in mid-August 2019. During these investigations, prospective and retrospective active case finding was carried out.

Food source and molecular typing identified the source within 10 days

After the outbreak was discovered in early August, epidemiological interviews and whole-genome sequencing clarified the food source and the respective listeria strain within 10 days. The investigation included sampling of food and surrounding potentially exposed surfaces in food establishments, including factories, markets and grocery stores, bars and restaurants. Some patients also provided food samples from home.

Regional health authorities issued a public health alert on August 15 after three cases of food poisoning were initially reported in early August. During interviews with patients, most of them mentioned that they had purchased stuffed pork from a variety of grocery stores -; mainly supermarkets and bars. Based on these responses, a traceability investigation at a mentioned grocery store pointed to a specific facility where the stuffed pork was produced.

The grocery store sold two different brands of pork, each produced by a different company. A sample of these products tested positive for L. monocytogenes. Food production at the facility with a Listeria-positive food sample was halted and a recall order was extended to meat or meat derivatives produced there. The tender was gradually amended to include all food produced at this facility.

While the facility distributed almost exclusively in Andalusia, the food recall affected an estimated 8 tons of meat products. Following the product recall, listeriosis reports decreased, suggesting that food products from other establishments did not play a significant role as a potential source in this outbreak.

Specific post-exposure protocol for pregnant women: 30,000 women were surveyed

A total of 3,582 suspected cases were investigated, 207 were confirmed and 3,059 were classified as probable cases. In almost all patients (94%) with confirmed listeriosis, an invasive clinical form of the disease was observed and two out of three (68%) required hospitalization. The authors also report three deaths associated with this outbreak and five miscarriages out of 34 pregnant patients.

Fernández-Martínez et al. describe the protocol for antibiotic post-exposure prophylaxis (PEP) in pregnant women with a history of stuffed pork consumption (after antimicrobial susceptibility testing, ampicillin resistance was excluded in the outbreak strain). This included a follow-up examination to see whether the women developed symptoms of listeriosis.

Within weeks of the outbreak, more than 30,000 pregnant women across Andalusia were interviewed by authorities. Based on an individual assessment, approximately 5% of these women were recommended PEP. According to the authors, the protocol for this particular outbreak was designed to limit the potential impact on pregnant women.

By the end of the outbreak in October 2019, more than 1,800 food establishments had been inspected and 87 non-human samples were found to be contaminated with L. monocytogenes. Most positive samples came from foods containing stuffed pork (n=76) and other pork derivatives (n=6).

As Fernández-Martínez et al. Note that ready-to-eat (RTE) products "can be consumed without prior heating and their consumption is increasing, they are quickly becoming a relevant vehicle for listeriosis outbreaks. In Andalusia, stuffed pork is already very popular, an inexpensive, traditional RTE food. It consists of a cold cut of fried pork with garlic, spices and salt. It is often served in summer and Consumed on special occasions, it is one of the most popular “tapas” and a common ingredient in aperitifs and sandwiches.” According to their research, an outbreak with 200 or more confirmed cases in Europe dates back to 1992, when 279 confirmed cases of listeriosis linked to the consumption of jellied pork tongue were recorded in France.

The authors argue that “efforts to incorporate whole genome sequencing” into outbreak investigations and coordinate various sectors at regional and national levels are essential for the prevention and control of listeriosis.

Source:

European Center for Disease Prevention and Control (ECDC)

Reference:

Fernández-Martínez, NF, et al. (2022) Listeriosis outbreak due to contaminated stuffed pork, Andalusia, Spain, July to October 2019. Eurosurveillance. doi.org/10.2807/1560-7917.ES.2022.27.43.2200279.

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