Prevalence of Asymptomatic SARS-CoV-2 Infection

Abstract

TO THE EDITOR: Oran and Topol s narrative review (1) is commendably useful for being one of the first attempts to estimate the proportion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) carriers who are asymptomatic. However, their conclusion that therefore “asymptomatic SARS-CoV-2 infection . . . is a significant factor in the rapid progression of [coronavirus disease 2019 (COVID-19)]” seems to be utterly unsubstantiated. This is surprising considering Annals normally rigorous peerreview standards. Oran and Topol s assertion in the abstract that “asymptomatic persons . . . can transmit the virus” is supported by only 2 data. They claim that the authors of an Italian study “confirmed that several new cases of SARS-CoV-2 infection . . . had been caused by exposure to asymptomatic persons.” However, the cited (non–peer-reviewed) article merely mentions that 2 or at most 3 of 8 persons studied “may [emphasis added] have become infected from an asymptomatic carrier” (2). For example, the authors of this study state, “Subject 5 reported meeting an asymptomatic infected individual before the lockdown.” Of note, the same study reported, “No infections were detected in . . . 234 tested children [younger than 11 years], despite . . . living in [the] same household as infected people.” This finding is consistent with other evidence that children are much less likely to become infected and, when infected, are typically asymptomatic (as opposed to presymptomatic) carriers (3, 4). The only other evidence cited by Oran and Topol to support the role of asymptomatic transmission comes from just 1 of the other 16 cohort studies they reviewed. They include the following statement from that study: “More than half of [infected nursing facility] residents . . . were asymptomatic at the time of testing and most likely contributed to transmission” (5). In fact, the cited study explains that “7 days after their positive test, 24 of 27 asymptomatic residents (89%) had onset of symptoms and were recategorized as pre-symptomatic.” Oran and Topol seem to have confused the same issue of asymptomatic versus presymptomatic transmission that they attempt to clarify at the beginning of their own review when they state, “To be clear, the asymptomatic individual . . . will never develop symptoms.” I ask that the Editors retract this review or at least request that the authors modify their perhaps unintentional but clearly misleading conclusion about the contagiousness of asymptomatic SARS-CoV-2 carriers. Any objective expert or careful reader surely would wonder whether the review s conclusion, which warns about “the high risk for silent spread by asymptomatic persons” and suggests that therefore “[m]edical practice and public health measures should be modified to address this challenge,” is in fact substantiated by the “data” cited by the authors (that is, that 2 or 3 persons in Italy who reported having had contact with asymptomatic carriers may thus have become infected). This review and in particular its dubiously substantiated conclusion have been widely cited—including in many reports asserting that “up to 45% of all Covid-19 infections are from asymptomatic persons” (4)—and therefore urgently require correction.