Invasive listeriosis in Southern Switzerland: A local problem that is actually global

To the Editor—Recently, Conrad et al [1] reported 10 cases of Listeria monocytogenes invasive disease with 3 deaths in a 6-year time frame (2010–2015). Whole-genome sequencing (WGS) demonstrated a link to a widely distributed brand of ice cream, which enabled the source to be narrowed to 2 production facilities, indicating long-standing contamination. We describe here an outbreak of 6 cases of invasive L. monocytogenes infections in Ticino region (a canton of approximately 350 000 inhabitants in the south of Switzerland, close to the Italian border) from July to September 2022. Table 1 provides the demographic and clinical characteristics of the patients; note that 4 patients had L. monocytogenes serotype 4b, and 2 had serotype 1/2b. Some weeks before this outbreak, a similar event occurred in Italy [2]; 2 patients, both infected with serotype 4b, had bought fresh cheese in Italy from the same grocery store. However, WGS of the isolates was not performed, so we could not establish whether the strains were related or identify a common source. As for the remaining patients, they denied assumption of cheese or pork derivate in the weeks before hospitalization, and cohabitants did not refer symptoms correlated with L. monocytogenes infection.