Reconstruction of Transmission Pairs for Novel Coronavirus Disease 2019 (COVID-19) in Mainland China: Estimation of Superspreading Events, Serial Interval, and Hazard of Infection

Abstract

Background: Knowledge on the epidemiological features and transmission patterns of novel coronavirus disease (COVID-19) is accumulating. Detailed line-list data with household settings can advance the understanding of COVID-19 transmission dynamics.

Methods: A unique database with detailed demographic characteristics, travel history, social relationships, and epidemiological timelines for 1407 transmission pairs that formed 643 transmission clusters in mainland China was reconstructed from 9120 COVID-19 confirmed cases reported during 15 January-29 February 2020. Statistical model fittings were used to identify the superspreading events and estimate serial interval distributions. Age- and sex-stratified hazards of infection were estimated for household vs nonhousehold transmissions.

Results: There were 34 primary cases identified as superspreaders, with 5 superspreading events occurred within households. Mean and standard deviation of serial intervals were estimated as 5.0 (95% credible interval [CrI], 4.4-5.5) days and 5.2 (95% CrI, 4.9-5.7) days for household transmissions and 5.2 (95% CrI, 4.6-5.8) and 5.3 (95% CrI, 4.9-5.7) days for nonhousehold transmissions, respectively. The hazard of being infected outside of households is higher for people aged 18-64 years, whereas hazard of being infected within households is higher for young and old people.

Conclusions: Nonnegligible frequency of superspreading events, short serial intervals, and a higher risk of being infected outside of households for male people of working age indicate a significant barrier to the identification and management of COVID-19 cases, which requires enhanced nonpharmaceutical interventions to mitigate this pandemic.

Keywords: COVID-19; hazard of infection; serial interval; superspreading event; transmission.

Figure 1.

COVID-19 transmission clusters. A, Six hundred forty-three transmission clusters, stratified by the size of cluster n. Red, green, and blue nodes denote primary cases, household secondary cases, and nonhousehold secondary cases, respectively. B, Empirical offspring distribution for the number of secondary cases infected by each of the 809 primary cases. C, Empirical and estimated serial interval distributions for household or nonhousehold transmissions. Pink and blue bars indicate the empirical distributions of serial interval data for household and nonhousehold transmissions, respectively. Red curve indicates the estimated serial interval distributions for household transmissions, based on the posterior median estimates of the mean and standard deviation (SD) of normal distribution. Blue curve indicates the estimated serial interval distributions for nonhousehold transmissions, based on the posterior median estimates of the mean and SD of normal distribution. Fitting results with alternative distributions (eg, Gumbel or Logistic distribution) are available in Supplementary Tables 3–5.