Invasive listeriosis is a rare foodborne disease with a large public health impact, because of the severity of its clinical manifestations and high fatality rate. In this study, we provide a snapshot of epidemiology of listeriosis in Lombardy Region, Northern Italy, reviewing enhanced surveillance data collected over fourteen years, after the implementation of a voluntary laboratory-based surveillance system for the referral of clinical isolates of Listeria monocytogenes to a regional reference laboratory, since 2005.
Invasive listeriosis cases data from 2005 to 2018 were extracted from the regional laboratory-based surveillance system database and compared with the regional mandatory notification disease system data.
Over the fourteen period under study, 533 Listeria monocytogenes isolates were detected by the laboratory surveillance system, 55 of which from pregnancy-related cases. The median age of non-pregnancy-associated patients was 71 years, with 64.6% of cases observed in the elderly. Cases with underlying medical risk conditions accounted for 92.1%, and the fatality rate was 26.2%. By integrating data from the two sources, a total of 935 cases were recorded. The collection of data through the laboratory surveillance system allowed to increase the surveillance sensitivity by 18%.
Our results documented the growing epidemiological relevance of listeriosis through the analysis of two information sources. The data we obtained were consistent with the literature, except for pregnancy-related cases, which are often underdiagnosed. This study highlighted the importance of laboratory-based surveillance system, which led to a significant increase in the sensitivity of the mandatory notification system.
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 The Integrated Rapid Infectious Disease Analysis (IRIDA) Advanced Research Infrastructure for Experimentation in GenomicS (ARIES) Platform. Available at: https://irida.iss.it. Accessed on: 22/12/2019.