Table 1. Description of serum groups used for IgM measurements.

Group	N	Characteristics	N	Origin	Year of sample collection	Diagnosis
						PCR	Neutralization test	IgM ELISA	IgG ELISA
DENV	54	Acute sera from returning travelers and DENV endemic regions	12	Italy	2013–2016	10	4	12	7
			2	Zeptometrix		0	2	2	2
			4	Seracare (Colombia, Honduras, Equador)	2011	0	4	4	4
			17	Sri Lanka	2015	17	0	17	n.t.
			19	Germany	2011–2016	14	0	19	18
ZIKV	16	Acute sera from returning travelers and DENV endemic regions	2	Brazil	2015–2016	1	1	2	2
			8	Italy	2015–2016	6	2	8	7
			6	Germany	2016–2017	4	1	6	6
WNV	16	Residents in WNV endemic regions	16	Italy	2012–2013	0	16	16	16

Abbreviation: not tested, n.t.

Diagnosis was performed at the laboratories supplying the samples for this study, using commercial and in house assays.