A study conducted by the European Center for Disease Prevention and Control (ECDC) has found that most listeriosis outbreaks go undetected.

ECDC’s research looked at 2,726 human Listeria monocytogenes isolates from 27 countries between 2010 and 2015. Less than half of the cases were isolated, while the other half of cases were clustered together.

Around one-third of the cases that belonged to a cluster had appeared in more than one country, many times lasting for several years. But somehow, only two listeriosis outbreaks were reported in the EU in 2016, and five were reported in 2015. Based on these findings, many of the listeriosis cases went undetected.

To better and more quickly identify these illnesses, researchers believe that whole-genome sequencing is the answer. Specifically, they believe that using WGS to characterize listeriosis cases at the EU-level could speed up the detection of clusters by up to 5 months, when compared to epidemiological investigation at country level. Ideally, this would slow down the pace of an outbreak caused by the same, common food source.

“This study is a milestone on the way to tackling listeriosis in Europe. With this new collaborative effort with the Member States, we have revealed the related nature of many cases of severe listeriosis. We are now strengthening routine surveillance by introducing the collection and analysis of whole-genome sequencing data from all reported human listeriosis cases”, says ECDC’s chief scientist Mike Catchpole.

“Improving our surveillance on Listeria cases will save lives, particularly among vulnerable population groups such as the elderly and also pregnant women, who may pass on the bacteria to the fetus if they consume contaminated food,” says Catchpole.

Cases of listeriosis have continued to increase in the EU since 2008. In 2016, the most recent year for which data are available, the EU experienced 2,536 listeriosis cases and 247 deaths.

ECDC's study has been published in Eurosurveillance, a peer-reviewed journal.

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