Table 1.

Shigella sp. isolates used in this study

Species/Serotype	Isolate set	Reference	Selected	Function in this study	Number
S. flexneri 2a	English representative subsample, 2008–2014	This study	Representatively 9% (32 of 368 cases) of travel, 18% (147 of 820 cases) of non-travel-associated cases	Primary data set under study	179
	French representative subsample, 2009–2014	This study	Representative of isolates received	Determine whether English MSMA sublineages were present internationally	40
S. sonnei	English representative subsample, 2008–2014	This study	Representatively 3% (45 of 1539 cases) of travel, 8% (142 of 1751 cases) of non-travel-associated cases. Age-restricted (16–60 years old) to explore circulation in adults.	Primary data set under study	187
	French representative subsample, 2009–2014	This study	Representative of isolates received	Determine whether MSMA sublineages were present internationally	75
	UK 2015/16 MSMA clusters	22	Identified as MSMA clusters, see reference	Determine whether MSMA sublineages identified in English representative subsample remained in circulation in 2015/16	50
S. flexneri 3a	MSMA sublineage isolates	19	Representatively 20% of all isolates, see reference	Used to examine the horizontal transmission of pKSR100	206
				Total	737
				Total (this study)	481

English isolates were supplied by the Gastrointestinal Bacteria Reference Unit at Public Health England, London. For the English representative subsample, non-travel-associated isolates were intentionally over-represented and travel-associated isolates were included to provide temporally-relevant context. French isolates were supplied from the French National Reference Centre for E. coli, Shigella and Salmonella at the Institut Pasteur, Paris