Could asymptomatic carriers spread the SARS-CoV-2 infection? Experience from the Italian second wave

Excerpt

We read with great interest the recent paper by Shiyi Cao et al. [1] entitled “Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China” regarding the mass screening program of SARS-CoV-2 infection conducted in the metropolitan city of Wuhan, China. The authors reported the organization process, detailed technical methods used, and results of this citywide nucleic acid screening in which nearly 10 million people were recruited. This impressive screening program, conducted to evaluate the current status of infection at a given post-lockdown time point, provides a unique/extraordinary insight on the current status of the coronavirus pandemic. The authors reported 300 new asymptomatic positive cases and, in addition, 107 out 34424 previously recovered COVID-19 cases tested positive again. Interestingly, the authors highlighted that for all positive cases no “viable virus” was detected on cultures and all their close contacts tested negative for the COVID-19, which suggested the lack of evidence of transmission from asymptomatic cases. Although mass screening programs are a valid and extremely useful tools to collect important information with a high number of samples, we believe that the claims should be evaluated in the light of and compared to currently available data as well as the data cited in the article itself. There is a contradiction between the authors’ conclusions and current health recommendations for preventing the spread of COVID-19 coupled with existing literature regarding SARS-CoV-2 transmission [2]. Data suggests and has taught us [3] that even among presymptomatic patients, the high levels of viral shedding in the upper respiratory tract are a key factor in the transmissibility of the infection. In addition, the viral loads of SARS-CoV-2 were found similarly high in the four canonical symptomatic groups (presymptomatic, asymptomatic, typical symptoms and atypical symptoms); SARS-CoV-2 spreads in high concentrations from the nasal cavities prior to symptom development and viable virus was found in culture also in presymptomatic cases [4]. Additional evidence cautions on the existence of transmissibility of the asymptomatic cases as an alarm signal: He et al. argue that the transmissibility of asymptomatic cases could be lower than that of the symptomatic case [5] and Chen et al. reported no statistical difference in the transmissibility of asymptomatic cases versus symptomatic cases among close contacts [6]. …