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.