Table 1

Reported infectious period (IP) for asymptomatic cases (T5 parameter) from virological studies where serial diagnostic tests were undertaken to infer IP; tracking studies where IP is inferred from contact tracing; modelling studies where IP is reported as a prior (assumed parameter value) or a posterior estimate

StudyCountriesParameter (days)NCentral tendency reportedVariation (days; inclusion)Comment
Virological studies
Zhou et al 74 China11 days1MaxThis study serially swabbed and tested symptomatic (17) and asymptomatic (1) cases via RT-PCR. The single asymptomatic case tested positive up to 11 days postcontact with an infected patient (presumed point of exposure).
Hu et al 7 China9.5 days24Median1–21 rangeSerial testing. Period between ‘onset’ (where onset relates to first positive test) and clearance, adjudged via two negative RT-PCR tests, deemed by the authors to be the ‘communicable period’. IQR: 3.5–13.
Tracking studies
Ma et al 8 China, Germany, Japan, Singapore, South Korea, Malaysia and Vietnam7.25 days*49Mean95% CI 5.91 to 8.69*Ma et al do not report infectious period for asymptomatic cases explicitly within their paper. The authors estimated the infectious period as the upper estimated latent period minus the serial interval, using a dataset of 1155 cases from several countries (latent period was estimated with 11 infector–infectee pairs; serial interval was estimated from 689 infector–infectee pairs).
Ma et al reported a mean upper limit of latent period of 2.52 days; the mean serial interval for asymptomatic cases (using date of diagnosis for onset) was estimated to be 9.77 (94% CI 8.43 to 11.21).
Hu et al 7 China34–9 rangeCluster of infection within a family, where the primary case was asymptomatic. The transmissions to secondary cases occurred over a period 4–9 days post the presumed point of exposure for the primary case.
Modelling studies
Li et al 27 China3.5* (posterior from a model estimating duration for undocumented cases)Median95% CI 3.19% to 3.78%Li et al do not explicitly attempt to model asymptomatic cases, or their infectious duration. Instead the population infected is divided into ‘documented’ and ‘undocumented’. Documented were all cases where patients had symptoms severe enough to be confirmed infected; all other cases were considered undocumented. Therefore, this estimate represents asymptomatic and ‘mild’ cases. The 95% CI around the median infectious period estimate was 3.19 to 3.78
Tuite et al 26 39 Canada6–6.5 (prior)(Fixed parameter within a deterministic model)Mathematical model (deterministic), with a fixed parameter estimate of 6 or 6.5 days. Important to note that duration for ‘mild’ was equal to severe cases.
Davies et al 14 UK7 days (prior)MeanModel with asymptomatic infection compartment. Modelled with a gamma distribution, beta 1.4; alpha 5. Despite the subclinical aspect of this parameter, it could be considered analogous to total infectious period without intervention.
Davies et al 15 UK5 days (prior)MeanModel with asymptomatic infection compartment. Modelled with a gamma distribution, k=4. Authors: ‘Assumed to be the same duration as total infectious period for clinical cases, including preclinical transmission’.
  • RT-PCR, reverse transcriptase PCR.