Presymptomatic transmission of SARS-CoV-2 infection: a secondary analysis using published data

Abstract

Objective: To estimate the proportion of presymptomatic transmission of SARS-CoV-2 infection that can occur, and the timing of transmission relative to symptom onset.

Setting/design: Secondary analysis of international published data.

Data sources: Meta-analysis of COVID-19 incubation period and a rapid review of serial interval and generation time, which are published separately.

Participants: Data from China, the Islamic Republic of Iran, Italy, Republic of Korea, Singapore and Vietnam from December 2019 to May 2020.

Methods: Simulations were generated of incubation period and of serial interval or generation time. From these, transmission times relative to symptom onset, and the proportion of presymptomatic transmission, were estimated.

Outcome measures: Transmission time of SARS-CoV-2 relative to symptom onset and proportion of presymptomatic transmission.

Results: Based on 18 serial interval/generation time estimates from 15 papers, mean transmission time relative to symptom onset ranged from -2.6 (95% CI -3.0 to -2.1) days before infector symptom onset to 1.4 (95% CI 1.0 to 1.8) days after symptom onset. The proportion of presymptomatic transmission ranged from 45.9% (95% CI 42.9% to 49.0%) to 69.1% (95% CI 66.2% to 71.9%).

Conclusions: There is substantial potential for presymptomatic transmission of SARS-CoV-2 across a range of different contexts. This highlights the need for rapid case detection, contact tracing and quarantine. The transmission patterns that we report reflect the combination of biological infectiousness and transmission opportunities which vary according to context.

Keywords: epidemiology; infection control; infectious diseases; public health; virology.

Figure 1

Schematic illustration of incubation period, generation time and serial interval at transmission pair level. Scenario A: if transmission occurs after symptom onset, mean generation time/serial interval is longer than mean incubation period. Scenario B: if presymptomatic transmission occurs, mean generation time/serial interval is shorter than mean incubation period. Scenario C: a negative serial interval is possible if symptoms manifest in the infectee before the infector. Relevant to all scenarios, if incubation period is assumed to be independent and identically distributed, mean serial interval will approximate mean generation time.

Figure 2

A summary of how serial interval and generation time estimates were selected for analyses.

Figure 3

A summary of country or region and date ranges for the 18 serial interval and generation time estimates from 15 papers that were included in simulations to infer presymptomatic transmission. Line thickness is scaled to reflect sample size (ie, Kwok et al have the smallest and Xu et al the largest sample size). CN AEH, China: all regions excluding Hubei; CN HK, China: Hong Kong; CN SY, China: Shiyan (Hubei); CN SZ, China: Shenzhen; CN TJ, China Tianjin; CN ZH, China: Zhuhai; IR, Iran; IT, Italy; KR, The Republic of Korea; SG, Singapore; VN, Vietnam.

Figure 4

A summary of the parameters from the serial interval and generation time estimates that were used in the simulation, by country or region and reference. Points indicate means and bars indicate 95% CIs. CN AEH, China: all regions excluding Hubei; CN HK, China: Hong Kong; CN SY, China: Shyan (Hubei); CN SZ, China: Shenzhen; CN TJ, China Tianjin; CN ZH=China: Zhuhai; IR, Iran; IT, Italy; KR, The Republic of Korea; SG, Singapore; VN, Vietnam.

Figure 5

A boxplot summarising simulation results showing transmission time in days relative to infector symptom onset. Purple triangles represent the mean of the simulation samples. CN AEH, China: all regions excluding Hubei; CN HK, China: Hong Kong; CN SY, China: Shiyan (Hubei); CN SZ, China: Shenzhen; CN TJ, China Tianjin; CN ZH, China: Zhuhai; IR, Iran; IT, Italy; KR, The Republic of Korea; SG, Singapore; VN, Vietnam.