title: Tracing sources of Listeria contamination in traditional Italian cheese associated with a US outbreak: investigations in Italy.
abstract: In 2012 a US multistate outbreak of listeriosis was linked to ricotta salata imported from Italy, made from pasteurized sheep's milk. Sampling activities were conducted in Italy to trace the source of Listeria monocytogenes contamination. The cheese that caused the outbreak was produced in a plant in Apulia that processed semi-finished cheeses supplied by five plants in Sardinia. During an 'emergency sampling', 179 (23·6%) out of 758 end-products tested positive for L. monocytogenes, with concentrations from <10 c.f.u./g to 1·1 × 106 c.f.u./g. Positive processing environment samples were found in two out of four processing plants. A 'follow-up sampling' was conducted 8 months later, when environmental samples from three out of six plants tested positive for L. monocytogenes and for Listeria spp. PFGE subtyping showed 100% similarity between US clinical strains and isolates from ricotta salata, confirming the origin of the outbreak. The persistence of strains in environmental niches of processing plants was demonstrated, and is probably the cause of product contamination. Two PFGE profiles from clinical cases of listeriosis in Italy in 2011, stored in the MSS-TESSy database, were found to have 100% similarity to one PFGE profile from a US clinical case associated with the consumption of ricotta salata, according to the US epidemiological investigation (sample C, pulsotype 17). However, they had 87% similarity to the only PFGE profile found both in the US clinical case and in 14 ricotta cheese samples collected during the emergency sampling (sample B, pulsotype 1). Sharing of molecular data and availability of common characterization protocols were key elements that connected the detection of the US outbreak to the investigation of the food source in Italy. Simultaneous surveillance systems at both food and human levels are a necessity for the efficient rapid discovery of the source of an outbreak of L. monocytogenes.
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: V A
authors.initials: VA
authors.lastname: Acciari
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: L
authors.initials: L
authors.lastname: Iannetti
authors.affiliation: Istituto Superiore di Sanità,Roma,Italy.
authors.forename: A
authors.initials: A
authors.lastname: Gattuso
authors.affiliation: Istituto Superiore di Sanità,Roma,Italy.
authors.forename: M
authors.initials: M
authors.lastname: Sonnessa
authors.affiliation: Istituto Superiore di Sanità,Roma,Italy.
authors.forename: G
authors.initials: G
authors.lastname: Scavia
authors.affiliation: Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata,Struttura Complessa Territoriale di Putignano (BA),Italy.
authors.forename: C
authors.initials: C
authors.lastname: Montagna
authors.affiliation: Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata,Struttura Complessa Territoriale di Putignano (BA),Italy.
authors.forename: N
authors.initials: N
authors.lastname: Addante
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: M
authors.initials: M
authors.lastname: Torresi
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: L
authors.initials: L
authors.lastname: Zocchi
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: S
authors.initials: S
authors.lastname: Scattolini
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: P
authors.initials: P
authors.lastname: Centorame
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: C
authors.initials: C
authors.lastname: Marfoglia
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale',National Reference Laboratory for Listeria monocytogenes,Teramo,Italy.
authors.forename: V A
authors.initials: VA
authors.lastname: Prencipe
authors.affiliation: Istituto Superiore di Sanità,Roma,Italy.
authors.forename: M V
authors.initials: MV
authors.lastname: Gianfranceschi
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D002611:Cheese / Q000382:microbiology*; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D005511:Food Handling; D005516:Food Microbiology; D007558:Italy; D008089:Listeria monocytogenes / Q000145:classification / Q000302:isolation & purification*; D008088:Listeriosis / Q000453:epidemiology* / Q000382:microbiology; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D014481:United States / Q000453:epidemiology
chemical_list: D001426:Bacterial Proteins
keywords: Food safety; Listeria; molecular epidemiology; outbreaks; surveillance system