The nasopharyngeal swab molecular test is the diagnostic tool par excellence for recognising SARS-CoV-2 infection.

In Western countries, public health and biomedical research agencies recommend it even for asymptomatic individuals following a positive serological test. However, so far,there is insufficient data available to determine whether the presence of SARS-CoV-2 antibodies in the serum of an asymptomatic individual can influence the outcome of the molecular test performed by nasopharyngeal swab.

In a paper recently published in the scientific journal Lancet Microbe, a group of researchers from Sapienza University of Rome, including Guido Antonelli from the Department of Molecular Medicine, investigated this issue to assess the actual need for such a procedure for anti-SARS-CoV-2 antibody-positive subjects.

Specifically, during an epidemiological study aimed at investigating the prevalence of infection in defined groups of workers, including healthcare workers, the researchers verified the presence of anti-SARS-CoV-2 antibodies in approximately 16,500 people involved in screening programmes conducted at the Sapienza Policlinico Umberto I General Hospital in 2020.

The protocol required subjects who tested positive for anti-SARS-CoV-2 antibodies to undergo a nasopharyngeal swab to determine the presence of the virus in respiratory secretions: the results of the study showed that of 212 participants who tested positive for anti-SARS-CoV-2 antibodies, only one tested positive for the molecular swab, i.e. less than 1%.

"Our work highlights how this procedure is redundant and inappropriate in the context of an epidemiological survey in which all participants are asymptomatic," explains Guido Antonelli. "Moreover, the data is extremely interesting from a practical point of view because, given the progressive increase in the number of people who are seropositive for anti-SARS-CoV-2 antibodies, it facilitates the optimisation and rationalisation of the use of so-called molecular swabs".   

Riferences:

Asymptomatic individuals positive for anti-SARS-CoV-2 antibodies negative on molecular swab - Guido Antonelli, Emanuela Anastasi, Fabrizio Ciprani, Rodolfo J Riveros Cabral, Cristiano Ialongo, Maria R Capobianchi, Ombretta Turriziani, Antonio Angeloni - Lancet Microbe 2021 May;2(5):e178.  doi: 10.1016/S2666-5247(21)00083-5 

Further Information

Guido Antonelli
Department of Molecular Medicine,
guido.antonelli@uniroma1.it