Ongoing outbreak of invasive listeriosis, Germany, 2012 to 2015

The source of the causative food vehicle has not been elucidated yet.

Listeriosis patient isolates in Germany have shown a new identical pulsed-field gel electrophoresis (PFGE) pattern since 2012 (n = 66). Almost all isolates (Listeria monocytogenes serotype 1/2a) belonged to cases living in southern Germany, indicating an outbreak with a so far unknown source. 

Case numbers in 2015 are high (n = 28). No outbreak cases outside Germany have been reported. 

Next generation sequencing revealed the unique cluster type CT1248 and confirmed the outbreak.

Investigations into the source are ongoing. Since November 2012, a previously not observed pulsed-field gel electrophoresis (PFGE) pattern in human isolates of invasive L. monocytogenes serotype1/2a has been detected in Germany with increasing frequency. Altogether 66 outbreak cases have been recorded, with 28 cases in 2015. Four cases were pregnancy-associated and six cases died in the course of the disease. Here we provide details of the ongoing outbreak.

Outbreak description: Since 2009, all German Listeria isolates submitted to the National Reference Centre (NRC) for Salmonella and other bacterial enterics at the Robert-Koch Institute (RKI) or to the Austrian-German binational reference laboratory (KL) for Listeria at the Austrian Agency for Health and Food Safety (AGES), have been tested with PFGE for clonal relationship. Submission of isolates is encouraged by public health authorities but is voluntary without legal obligation. 

Between November 2012 and November 2015, altogether 793 isolates from notified listeriosis cases were typed, which accounted for 45% of all cases in that period (n=1,765). In southern Germany, this proportion was higher (ca 60%) and since 2012, human isolates of L. monocytogenes serotype 1/2a with the NRC internal nomenclature of the AscI/Apa I pattern 13a/54 have been observed.

Regarding the source of the causative food vehicle, the results showed a heterogeneous picture. Until now, we have not observed cases with an epidemiological link to an institution (e.g. hospital infection). Preliminary results largely exclude fish and cheese products as a possible source but this has to be complemented by systematic screening of Listeria isolates collected from food. Based on sequencing results, a PCR protocol aiming to detect CT1248 was developed for screening of isolates and published on the KL website. 

Source:http://www.eurosurveillance.org/images/dynamic/EE/V20N50/art21336.pdf