Characterization of A Staphylococcal Food Poisoning Outbreak in A Workplace Canteen during the Post-Earthquake Reconstruction of Central Italy

Abstract

In summer 2017, a foodborne outbreak occurred in Central Italy, involving 26 workers employed in the post-earthquake reconstruction. After eating a meal provided by a catering service, they manifested gastrointestinal symptoms; 23 of them were hospitalized. The retrospective cohort study indicated the pasta salad as the most likely vehicle of poisoning. Foods, environmental samples, and food handlers' nasal swabs were collected. <i>Bacillus cereus</i> (<i>Bc</i>) and coagulase-positive staphylococci (CPS) including <i>S. aureus</i>, together with their toxins, were the targets of the analysis. CPS, detected in all the leftovers, exceeded 10⁵ CFU/g in the pasta salad, in which we found Staphylococcal Enterotoxins (SEs) (0.033 ng SEA/g; 0.052 ng SED/g). None of the environmental and human swabs showed contamination. We characterized 23 <i>S. aureus</i> from foods. They all belonged to the human biotype, showed the same toxigenic profile (<i>sea</i>, <i>sed</i>, <i>sej</i>, and <i>ser</i> genes), and had the same Pulsed Field Gel Electrophoresis (PFGE) pattern; none of them harbored <i>mecA</i> or <i>mupA</i> genes. We also detected <i>Bc</i> contamination in the pasta salad but none of the isolates harbored the <i>ces</i> gene for the emetic toxin cereulide. The EU Reference Laboratory for CPS confirmed the case as a strong-evidence outbreak caused by the ingestion of SEs produced by a single strain of <i>S. aureus</i> carried by the same human source. This outbreak was successfully investigated despite the emergency situation in which it occurred.