Evidence of SARS-CoV-2 antibodies and RNA on autopsy cases in the pre-pandemic period in Milan, Italy

Introduction. At the end of December 2019, the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing serious pneumonia was identified in Wuhan, Hubei Province, China. The coronavirus disease 2019 (COVID-19) viral disease rapidly spread worldwide, and the first laboratory-confirmed Italian COVID-19 case was identified in Lombardy on February 20, 2020. However, some recently performed studies have confirmed the virus circulation also in the pre-pandemic period. To date, no studies on this item have been conducted on autopsy cases. We, therefore, wanted to address this specific topic by analyzing blood samples collected from cadavers subjected to autopsy at the Institute of Legal and Forensic Medicine in Milan, Italy. Material and Methods. We selected all autopsy cases from 1st October 2019 to 27th March 2020 in which blood samples had been collected for judicial purpose. Three kind of test were carried out on each 3 ml sample: 1) PrimaLab rapid antigen serological test; 2) Elisa Wantai test; 3) Real-Time PCR test. The first two, albeit with different methodology, search for the presence in the blood of specific antibodies (IgM and IgG) produced by the immune system in response to the infection caused by SARS-CoV-2; the RT-PCR test, on the other hand, directly searches for the presence of SARS-CoV-2 viral RNA. Results. We enrolled a total of 169 cases. Out of these, at least one positive result among the three applied methods was observed in 5 cases (2 suicide by hanging and 3 natural death). In 4 of them, the positivity was observed with the PrimaLab rapid antigen test; in detail, 3 cases tested positive for specific SARS-CoV-2 IgM antibodies and 1 case for specific SARS-CoV-2 IgG antibodies. In only 1 case, a concomitant positivity both to the Elisa test and the RT-PCR analysis was observed. By integrating such findings with the epidemiological-forensic data, it was observed that 2 of the aforementioned cases (both IgM positive) referred to subjects who died in the second half of October 2019, 2 others (one IgM positive and the other one positive both to the Elisa and to the RT-PCR analyses) to subjects who died in the first half of December 2019 and, finally, the last one (IgG positive) to an individual who died in mid-January 2020. Discussion. Our study on samples collected before the first autochthonous case was detected in Italy confirms that SARS-COV-2 was already circulating since mid-October 2019. It also demonstrates that cadaveric blood samples may be a good substrate on which carry out tests for the searching of SARS-COV-2.