In this review, we discuss the evidence about the relative importance of these factors. A combination of viral, host, and environmental characteristics affect transmission. Transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), requires that a minimum but as yet unknown dose of replication-competent virus be delivered to a vulnerable anatomical site in a susceptible host. To date, there is 1 cluster of possible fecal–respiratory transmission. Vertical transmission occurs rarely transplacental transmission has been documented.Ĭats and ferrets can be infected and transmit to each other, but there are no reported cases to date of transmission to humans minks transmit to each other and to humans.ĭirect contact and fomite transmission are presumed but are likely only an unusual mode of transmission.Īlthough live virus has been isolated from saliva and stool and viral RNA has been isolated from semen and blood donations, there are no reported cases of SARS-CoV-2 transmission via fecal–oral, sexual, or bloodborne routes. Respiratory transmission is the dominant mode of transmission. The virus has heterogeneous transmission dynamics: Most persons do not transmit virus, whereas some cause many secondary cases in transmission clusters called “superspreading events.” Evidence-based policies and practices should incorporate the accumulating knowledge about transmission of SARS-CoV-2 to help educate the public and slow the spread of this virus. Infectiousness peaks around a day before symptom onset and declines within a week of symptom onset, and no late linked transmissions (after a patient has had symptoms for about a week) have been documented. In the few cases where direct contact or fomite transmission is presumed, respiratory transmission has not been completely excluded. ![]() Strong evidence from case and cluster reports indicates that respiratory transmission is dominant, with proximity and ventilation being key determinants of transmission risk. Although several experimental studies have cultured live virus from aerosols and surfaces hours after inoculation, the real-world studies that detect viral RNA in the environment report very low levels, and few have isolated viable virus. This article presents a comprehensive review of the evidence on transmission of this virus. ![]() Substantial evidence now supports preliminary conclusions about transmission that can inform rational, evidence-based policies and reduce misinformation on this critical topic. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of coronavirus disease 2019 (COVID-19), has spread globally in a few short months.
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