Investigation of a foodborne outbreak of Shigella sonnei in Ireland and Northern Ireland, December 2016: the benefits of cross-border collaboration and commercial sales data.

OBJECTIVES: To describe a cross-border foodborne outbreak of Shigella sonnei that occurred in Ireland and Northern Ireland (NI) in December 2016 whilst also highlighting the valuable roles of sales data and international collaboration in the investigation and control of this outbreak. STUDY DESIGN: A cross-border outbreak control team was established to investigate the outbreak. METHODS: Epidemiological, microbiological, and environmental investigations were undertaken. Traditional analytical epidemiological studies were not feasible in this investigation. The restaurant chain provided sales data, which allowed assessment of a possible increased risk of illness associated with exposure to a particular type of heated food product (product A). RESULTS: Confirmed cases demonstrated sole trimethoprim resistance: an atypical antibiogram for Shigella isolates in Ireland. Early communication and the sharing of information within the outbreak control team facilitated the early detection of the international dimension of this outbreak. A joint international alert using the European Centre for Disease Control's confidential Epidemic Intelligence Information System for Food- and Waterborne Diseases and Zoonoses (EPIS-FWD) did not reveal further cases outside of the island of Ireland. The outbreak investigation identified that nine of thirteen primary case individuals had consumed product A from one of multiple branches of a restaurant chain located throughout the island of Ireland. Product A was made specifically for this chain in a food production facility in NI. S. sonnei was not detected in food samples from the food production facility. Strong statistical associations were observed between visiting a branch of this restaurant chain between 5 and 9 December 2016 and eating product A and developing shigellosis. CONCLUSIONS: This outbreak investigation highlights the importance of international collaboration in the efficient identification of cross-border foodborne outbreaks and the value of using sales data as the analytical component of such studies.

Commonly used disinfectants fail to eradicate Salmonella enterica biofilms from food contact surface materials.

Salmonellosis is the second most common cause of food-borne illness worldwide. Contamination of surfaces in food processing environments may result in biofilm formation with a risk of food contamination. Effective decontamination of biofilm-contaminated surfaces is challenging. Using the CDC biofilm reactor, the activities of sodium hypochlorite, sodium hydroxide, and benzalkonium chloride were examined against an early (48-h) and relatively mature (168-h) Salmonella biofilm. All 3 agents result in reduction in viable counts of Salmonella; however, only sodium hydroxide resulted in eradication of the early biofilm. None of the agents achieved eradication of mature biofilm, even at the 90-min contact time. Studies of activity of chemical disinfection against biofilm should include assessment of activity against mature biofilm. The difficulty of eradication of established Salmonella biofilm serves to emphasize the priority of preventing access of Salmonella to postcook areas of food production facilities.

Investigation and management of an outbreak of Salmonella Typhimurium DT8 associated with duck eggs, Ireland 2009 to 2011.

Salmonella Typhimurium DT8 was a very rare cause of human illness in Ireland between 2000 and 2008, with only four human isolates from three patients being identified. Over a 19-month period between August 2009 and February 2011, 34 confirmed cases and one probable case of Salmonella Typhimurium DT8 were detected, all of which had an MLVA pattern 2-10-NA-12-212 or a closely related pattern. The epidemiological investigations strongly supported a linkbetween illness and exposure to duck eggs. Moreover, S. Typhimurium with an MLVA pattern indistinguishable (or closely related) to the isolates from human cases, was identified in 22 commercial and backyard duck flocks, twelve of which were linked with known human cases. A range of control measures were taken at farm level, and advice was provided to consumers on the hygienic handling and cooking of duck eggs. Although no definitive link was established with a concurrent duck egg-related outbreak of S. Typhimurium DT8 in the United Kingdom, it seems likely that the two events were related. It may be appropriate for other countries with a tradition of consuming duck eggs to consider the need for measures to reduce the risk of similar outbreaks.

Characterization of bacteriophages used in the Salmonella enterica serovar Enteritidis phage-typing scheme.

The 16 Salmonella enterica serovar Enteritidis (S. Enteritidis) typing phages (SETPs) used in the Laboratory of Enteric Pathogens (Health Protection Agency, London, UK) phage-typing scheme have not previously been characterized in detail. We have examined the adsorption properties of the phages with respect to a number of S. enterica serovars and defined phage morphology with electron microscopy. PFGE was used to estimate overall genome size and banding patterns generated by electrophoresis following restriction endonuclease digestion of the genome with HindIII were compared. PCR amplification and sequencing of selected genes was performed. The 16 phages comprise three morphotypes, Podoviridae (SETP1, 8, 10, 14, 15 and 16), Siphoviridae (SETP3, 5, 7, 11, 12 and 13) and Myoviridae (SETP2, 4, 6 and 9). All Podoviridae and Siphoviridae, but not Myoviridae, adsorbed to the O12 lipopolysaccharide antigen of Salmonella serogroups B (4,12) and D(1) (9,12). The genome sizes for the Podoviridae and Siphoviridae (PFGE-A) were approximately 42 kb. The genome size for Myoviridae SETP2, 4 and 9 was 36.5 kb, and for myovirus SETP6 was 27 kb. HindIII digestion of phage DNA produced 9 distinct patterns of 8 to 11 bands. Relationships between phages based on digest patterns were consistent with those defined by morphology. The Podoviridae had homologues of several P22 genes while the Siphoviridae had homologues of several genes present in the sequenced siphovirus SETP3 (EF177456). This study represents an initial step in characterizing the molecular basis that underlies the widely used S. Enteritidis typing scheme.

Salmonella enterica biofilm formation and density in the Centers for Disease Control and Prevention's biofilm reactor model is related to serovar and substratum.

Foodborne pathogens can attach to, and survive on, food contact surfaces for long periods by forming a biofilm. Salmonella enterica is the second most common cause of foodborne illness in Ireland. The ability of S. enterica to form a biofilm could contribute to its persistence in food production areas, leading to cross-contamination of products and surfaces. Arising from a large foodborne outbreak of S. enterica serovar Agona associated with a food manufacturing environment, a hypothesis was formulated that the associated Salmonella Agona strain had an enhanced ability to form a biofilm relative to other S. enterica. To investigate this hypothesis, 12 strains of S. enterica, encompassing three S. enterica serovars, were assessed for the ability to form a biofilm on multiple food contact surfaces. All isolates formed a biofilm on the contact surfaces, and there was no consistent trend for the Salmonella Agona outbreak strain to produce a denser biofilm compared with other strains of Salmonella Agona or Salmonella Typhimurium. However, Salmonella Enteritidis biofilm was considerably less dense than Salmonella Typhimurium and Salmonella Agona biofilms. Biofilm density was greater on tile than on concrete, polycarbonate, stainless steel, or glass.

Use of pulsed-field gel electrophoresis for comparison of similar but distinguishable isolates of Shigella sonnei collected in Ireland and Italy.

Comparison of pulsed-field gel electrophoresis patterns (generated with XbaI and BlnI) of Shigella sonnei isolates from Ireland and Italy suggests that two possibly distantly related lineages are present in both countries. Smaller, more closely related groups, including isolates from Ireland and Italy, were also noted. These groups raise the possibility that the dissemination of clonal groups of S. sonnei may have occurred in recent years.