According to a recent release by European Centre for Disease Prevention and Control, the current surveillance systems may not be picking up the fact that Listeria cases may be part of larger outbreak clusters. Because of this, large multi-country outbreaks may not be detected as fast as they should (or possibly at all).
Researchers "analysed 2 726 human
Listeria monocytogenes isolates from 27 countries between 2010 and 2015. It found that slightly under 50% of the cases are isolated whereas the remaining half of cases is clustered together. Around one third of the cases that were identified as part of a cluster affected more than one country, often lasting for several years. However, only two listeriosis outbreaks were reported in the EU in 2016 and five in 2015, which suggests that many of them have gone undetected."
The US continues to develop a strong system to track and identify outbreaks. Now using whole genome sequencing (WGS) allows distant cases to be clustered, making tracking more efficient. This is not yet the state of testing in the EU at this time.
European Centre for Disease Prevention and Control
https://ecdc.europa.eu/en/news-events/listeria-surveillance-new-eu-wide-study-reveals-most-outbreaks-remain-undetected
Listeria surveillance: new EU-wide study reveals that most outbreaks remain undetected
20 Aug 2018