A 2026 research analysis of four listeriosis outbreaks in Italy between 2022-2023 found that advanced DNA testing combined with teamwork between government agencies allowed health officials to quickly identify contaminated foods and stop outbreaks affecting over 100 people. The contaminated products included processed meats and olives, with pork-derived products identified as the primary source of Listeria bacteria in Europe.
Between 2022 and 2023, Italy experienced several serious outbreaks of listeriosis, a dangerous foodborne illness caused by bacteria found in contaminated food. Researchers studied how Italian health officials investigated and stopped these outbreaks, which affected over 100 people in one case. The contaminated foods included processed meats like frankfurters and mortadella, as well as black olives. By using advanced DNA testing and teamwork between different government agencies, officials were able to quickly identify where the bacteria came from and prevent more people from getting sick. This research shows how important it is for different organizations to work together when fighting foodborne illness outbreaks.
Key Statistics
A 2026 analysis of Italian outbreak investigations found that one Listeria outbreak in 2022 affected 101 people, making it one of the largest listeriosis outbreaks ever recorded in Italy, with contaminated foods including processed meats and black olives.
According to a 2026 research review of Italian listeriosis outbreaks, advanced DNA testing methods (cgMLST and SNP analysis) enabled health officials to rapidly identify contaminated food sources and distinguish between different bacterial strains causing separate outbreaks.
A 2026 Italian outbreak investigation study identified pork and pork-derived products as the primary reservoirs for Listeria transmission in Europe, consistent with European Food Safety Authority findings for 2023-2024.
Research reviewed by Gram found that three different genetic strains of Listeria caused four separate outbreaks in Italy between 2022-2023, with two strains (CC8 and CC155) increasingly implicated in European foodborne outbreaks in recent years.
The Quick Take
- What they studied: How Italian health officials investigated and stopped listeriosis outbreaks caused by contaminated food between 2022 and 2023
- Who participated: Four separate listeriosis outbreaks in Italy, with one outbreak involving 101 confirmed cases of illness from contaminated food
- Key finding: Advanced DNA testing combined with teamwork between different government agencies allowed officials to quickly identify contaminated foods (processed meats and olives) and stop the outbreaks
- What it means for you: Better outbreak investigation systems help protect you by finding contaminated foods faster and preventing more people from getting sick. However, this research focuses on how health systems work rather than what individual consumers should do
The Research Details
Italian health officials examined four separate listeriosis outbreaks that occurred between 2022 and 2023. They used advanced laboratory techniques called DNA analysis to identify exactly which strains of the Listeria bacteria caused each outbreak. The researchers documented how different government agencies—including food safety, public health, and agriculture departments—worked together to trace contaminated foods back to their sources.
The team used two main types of DNA testing: one method that compares large sections of bacterial DNA to track outbreaks across many people, and another method that looks at tiny differences in DNA to pinpoint exactly which food products were contaminated. This combination of techniques allowed them to identify the specific foods causing illness and understand how the bacteria spread.
The researchers also analyzed which types of Listeria bacteria were involved in each outbreak and compared their findings to what was happening in other European countries during the same time period.
Understanding how to investigate foodborne illness outbreaks quickly and effectively is crucial for protecting public health. When health officials can rapidly identify contaminated foods and their sources, they can remove those foods from stores and prevent more people from becoming ill. This research demonstrates that combining advanced laboratory testing with good communication between different government agencies makes outbreak investigations much more successful.
This research is based on real outbreak investigations conducted by Italian health authorities, making it highly relevant to food safety. The use of advanced DNA testing methods (cgMLST and SNP analysis) represents the current best practices in outbreak investigation. The study’s strength comes from examining multiple outbreaks and comparing findings with European data. However, the research focuses on how investigations were conducted rather than testing new prevention methods, so it cannot prove that one approach is definitively better than another.
What the Results Show
Italian health officials investigated four separate listeriosis outbreaks between 2022 and 2023. One outbreak was particularly large, affecting 101 people and making it one of the biggest listeriosis outbreaks ever recorded in Italy. The contaminated foods included processed meat products like chicken frankfurters, turkey frankfurters, mortadella (an Italian cured meat), and porchetta (roasted pork), as well as black olives.
The outbreaks were caused by different strains of Listeria bacteria belonging to three different genetic groups (called clonal complexes). One strain (CC1) is known worldwide as especially dangerous and typically causes severe illness. However, the other two strains (CC8 and CC155) have been increasingly causing outbreaks across Europe in recent years, suggesting they may be becoming more of a problem.
The advanced DNA testing methods proved essential to the investigation. By comparing the DNA of bacteria from sick people with bacteria found in food samples, officials could definitively prove which foods caused the outbreaks. This rapid identification allowed them to remove contaminated products from stores quickly and prevent additional cases.
The research highlighted the importance of cross-sector collaboration in outbreak response. When food safety agencies, public health departments, and agriculture authorities worked together and shared information quickly, investigations moved faster and were more successful. The study also found that pork and pork-derived products were the primary sources of Listeria bacteria in Europe during this period, which aligns with findings from the European Food Safety Authority.
According to Gram Research analysis, the findings align with what European health authorities have observed in recent years—that certain strains of Listeria (particularly CC8 and CC155) are becoming more common causes of foodborne outbreaks. The large size of the CC155 outbreak (101 cases) demonstrates that these strains can cause significant public health problems. The research confirms that processed meat products, particularly pork-derived items, remain a major source of Listeria contamination in Europe.
This research describes outbreak investigations that already happened rather than testing new prevention methods, so it cannot prove that one investigation approach works better than another. The study doesn’t include information about how many people might have been exposed to contaminated food but didn’t get sick. Additionally, the research focuses on Italian outbreaks, so findings may not apply exactly the same way in other countries with different food production systems or regulatory frameworks.
The Bottom Line
For food safety officials and public health agencies: Implement rapid DNA testing for outbreak investigations and establish clear communication channels between different government agencies. For consumers: Continue following basic food safety practices like cooking meat thoroughly, keeping raw and cooked foods separate, and refrigerating foods properly. The confidence level for these recommendations is high based on this research and established food safety practices.
Food safety officials, public health agencies, and government policymakers should prioritize implementing the outbreak investigation framework described in this research. Consumers should care about this research because it shows how health systems work to protect them from contaminated food. People at higher risk for severe listeriosis (pregnant women, elderly people, and those with weakened immune systems) should be especially careful about food safety.
Outbreak investigations typically take weeks to months to complete, depending on how widespread the contamination is. Once contaminated foods are identified and removed from stores, the number of new cases usually drops within days to weeks. Implementing better outbreak investigation systems at the national level could take several years.
Frequently Asked Questions
What is listeriosis and how do you get it from food?
Listeriosis is a serious infection caused by Listeria bacteria found in contaminated food. You get it by eating foods that contain the bacteria, particularly processed meats, deli products, soft cheeses, and sometimes vegetables. Cooking food thoroughly kills the bacteria.
Which foods are most likely to have Listeria bacteria?
According to research reviewed by Gram, pork-derived products like frankfurters, mortadella, and porchetta are primary sources of Listeria in Europe. Other high-risk foods include deli meats, soft cheeses, and unpasteurized dairy products. Proper refrigeration and cooking reduce risk.
How do health officials find the source of food poisoning outbreaks?
Health officials use advanced DNA testing to compare bacteria from sick people with bacteria in food samples. This allows them to identify exactly which foods caused illness. They also interview sick people about what they ate and work with food companies to trace products back to their sources.
Who is most at risk for serious listeriosis?
Pregnant women, elderly people over 65, and people with weakened immune systems face the highest risk of severe listeriosis. Healthy adults may have mild or no symptoms. Anyone experiencing fever, muscle aches, or nausea after eating potentially contaminated food should contact a doctor.
What should I do if I think I ate contaminated food?
Monitor yourself for symptoms like fever, muscle aches, nausea, and diarrhea for up to three weeks. Contact your doctor immediately if you develop these symptoms, especially if you’re pregnant, elderly, or have a weakened immune system. Check official food safety websites for recalls of products you purchased.
Want to Apply This Research?
- Track food purchases and storage dates for high-risk items (processed meats, deli products, soft cheeses) to maintain awareness of products that may be recalled due to contamination
- Set reminders to check food safety alerts and recalls weekly, and enable notifications for any recalls affecting products you regularly purchase
- Maintain a simple log of where you purchase high-risk foods and check official food safety websites monthly for recalls; report any suspicious food-related illness symptoms to your healthcare provider immediately
This research describes how health officials investigated past listeriosis outbreaks and does not provide medical advice. If you believe you have listeriosis or any foodborne illness, contact your healthcare provider immediately. Pregnant women, elderly individuals, and people with weakened immune systems should be especially cautious about food safety and consult their doctor about dietary precautions. This article is for informational purposes and should not replace professional medical or food safety guidance.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.