Table 2.

Considered retrospective studies that found no evidence for an early SARS-CoV-2 circulation

Reference	Methods	Samples	Study period and location	Findings	Caveats (#) and confirmations (§)
38	RT-PCR	631 nasopharyngeal swabs collected from outpatients with ILI by sentinel physicians within the regional influenza surveillance network	Nov 2019–Feb 2020 Lombardy (Italy)	No evidence of SARS-CoV-2 circulation	# Single methodological approach # Results not confirmed by another laboratory
37	RT-PCR	1581 respiratory samples collected within the framework of the regional influenza surveillance system	Nov 2019–Apr 2020 Lombardy (Italy)	First SARS-CoV-2 detection at the beginning of Mar	# Single methodological approach # Results not confirmed by another laboratory
39	RT-PCR	Mucus obtained from nasopharyngeal swabs collected from 166 patients with SARI	Nov 2019–Mar 2020 Rome (Italy)	No evidence of SARS-CoV-2 circulation	# Patients from an area not primarily involved during the first wave # Single methodological approach # Results not confirmed by another laboratory
41	RT-PCR	1683 oropharyngeal swabs from hospitalised patients with SARI	Nov 2019–Feb 2020 Liguria, Tuscany, Lazio, Puglia (Italy)	No evidence of SARS-CoV-2 circulation	# Patients from an area not primarily involved during the first wave # Single methodological approach # Results not confirmed by another laboratory
40	RT-PCR, metagenomic sequencing	5833 nasopharyngeal and oropharyngeal swabs collected from patients hospitalised for ILI	Nov 2019–Mar 2020 Valencia (Spain)	No evidence of SARS-CoV-2 circulation before Mar 2020	# Patients from an area not primarily involved during the first wave # Single methodological approach # Negative results not confirmed by another laboratory § The positive sample from March was confirmed by sequencing § The positivity was confirmed by another laboratory

ILI, influenza-like illness; RT-PCR, real-time PCR; SARI, severe acute respiratory illness.