Abstract
In June 2014, a staphylococcal food poisoning outbreak occurred at an international equine sports event in Luxembourg requiring the hospitalisation of 31 persons. We conducted a microbiological investigation of patients and buffet items, a case-control study and a carriage study of catering staff. Isolates of Staphylococcus aureus from patients, food and catering staff were characterised and compared using traditional typing methods and whole genome sequencing. Genotypically identical strains (sequence type ST8, spa-type t024, MLVA-type 4698, enterotoxin A FRI100) were isolated in 10 patients, shiitake mushrooms, cured ham, and in three members of staff. The case-control study strongly suggested pasta salad with pesto as the vehicle of infection (p<0.001), but this food item could not be tested, because there were no leftovers. Additional enterotoxigenic strains genetically unrelated to the outbreak strain were found in four members of staff. Non-enterotoxigenic strains with livestock-associated sequence type ST398 were isolated from three food items and two members of staff. The main cause of the outbreak is likely to have been not maintaining the cold chain after food preparation. Whole genome sequencing resulted in phylogenetic clustering which concurred with traditional typing while simultaneously characterising virulence and resistance traits.
Highlights
Food poisoning caused by enterotoxigenic Staphylococcus aureus is one of the most common foodborne diseases [1]
The bacteria may have been inactivated by heating the food prior to consumption and can be isolated neither from food nor the stool of the patient, the highly stable enterotoxins performed by S. aureus in the food may still be emetically active [6]
All 10 isolates obtained from patients’ stool samples represented the same genotype (MLST sequence type (ST)8, spa-type t024, MLVA-type 4698), possessed genes encoding sea allele FRI100 and conferring penicillin resistance mediated by blaZ
Summary
Food poisoning caused by enterotoxigenic Staphylococcus aureus is one of the most common foodborne diseases [1]. In France, which has a long-established foodborne disease surveillance system able to detect fairly rare events [2], staphylococcal food poisoning (SFP) has ranked in recent years as the first cause of foodborne outbreaks: of 1,288 reported foodborne outbreaks in. If a stool analysis is performed, the microbiological routine procedures often do not include testing for the presence of enterotoxigenic S. aureus unless requested by the physician [5]. The bacteria may have been inactivated by heating the food prior to consumption and can be isolated neither from food nor the stool of the patient, the highly stable enterotoxins performed by S. aureus in the food may still be emetically active [6]
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