Asymptomatic Transmission During the Coronavirus Disease 2019 Pandemic and Implications for Public Health Strategies

Abstract

SARS-CoV-2 spread rapidly within months despite global public health strategies to curb transmission by testing symptomatic patients and encouraging social distancing. Here, we summarize rapidly emerging evidence highlighting transmission by asymptomatic and pre-symptomatic individuals. Viral load of asymptomatic carriers is comparable to symptomatic patients, viral shedding is highest before symptom onset suggesting high transmissibility before symptoms. Within universally tested subgroups, surprisingly high percentages of COVID-19 positive asymptomatic individuals were found. Asymptomatic transmission was reported in several clusters. A Wuhan study showed an alarming rate of intrahospital transmission, and several countries reported higher prevalence among healthcare workers than the general population. This raises concern that health workers could act as silent disease vectors. Therefore, current public health strategies relying solely on ‘symptom onset’ for infection identification need urgent reassessment. Extensive universal testing irrespective of symptoms may be considered with priority placed on groups with high frequency exposure to positive patients.

Potential sources, modes of transmission and effectiveness of prevention measures against SARS-CoV-2

“…Irrespective of the frequency of asymptomatic carriers, they are considered to be important for the transmission of the disease [47]. Various studies reported SARS-CoV-2 infections, originating from asymptomatic carriers during close contacts such as household contacts or residents of a long-term care skilled nursing facility [43,[48][49][50][51][52]. Importantly, several studies have reported that viral RNA loads in pre-symptomatic, asymptomatic and symptomatic patients do not differ significantly [53][54][55].…”

Reflecting on the first two COVID-19 deaths in Uganda: a public health case study

“…This underlines the need for a change of approach from symptom-based screening, especially among staff at healthcare facilities. If no routine screening is done among HCW and support staff, we may fail to detect infectious cases leading to disastrous results [15,16].…”

Risk factors for the critical illness in SARS-CoV-2 infection: a multicenter retrospective cohort study

“…Limited by the retrospective nature of this study, it is not known whether these markers for in ammation and injuries increased around the time when severe symptoms presented. In addition, there seemed to be a mechanism for SARS-CoV-2 to escape the immune surveillance in certain patients as evidenced by the high prevalence of asymptomatic SARS-CoV-2 infected patients [21]. Therefore, another explanation is that in ammation and injuries were minimized because of immune evasion during the early disease course of critical COVID-19.…”