Characterizing superspreading potential of infectious disease: Decomposition of individual transmissibility

Abstract

In the context of infectious disease transmission, high heterogeneity in individual infectiousness indicates that a few index cases can generate large numbers of secondary cases, a phenomenon commonly known as superspreading. The potential of disease superspreading can be characterized by describing the distribution of secondary cases (of each seed case) as a negative binomial (NB) distribution with the dispersion parameter, k. Based on the feature of NB distribution, there must be a proportion of individuals with individual reproduction number of almost 0, which appears restricted and unrealistic. To overcome this limitation, we generalized the compound structure of a Poisson rate and included an additional parameter, and divided the reproduction number into independent and additive fixed and variable components. Then, the secondary cases followed a Delaporte distribution. We demonstrated that the Delaporte distribution was important for understanding the characteristics of disease transmission, which generated new insights distinct from the NB model. By using real-world dataset, the Delaporte distribution provides improvements in describing the distributions of COVID-19 and SARS cases compared to the NB distribution. The model selection yielded increasing statistical power with larger sample sizes as well as conservative type I error in detecting the improvement in fitting with the likelihood ratio (LR) test. Numerical simulation revealed that the control strategy-making process may benefit from monitoring the transmission characteristics under the Delaporte framework. Our findings highlighted that for the COVID-19 pandemic, population-wide interventions may control disease transmission on a general scale before recommending the high-risk-specific control strategies.

Transmission characteristics and inactivated vaccine effectiveness against transmission of the SARS-CoV-2 Omicron BA.2 variant in Shenzhen, China

“…SAI incidence was 15.8% among household contacts, which was not consistent with the incidence of SAI in Denmark in a published study (21). This may be because the local government in Shenzhen immediately compulsorily isolated household contacts at designated facilities after the index cases were diagnosed, resulting in a relatively low secondary attack rate compared with published study in Denmark (21). In addition, we observed that individuals who received booster vaccination had a lower risk of SAI compared with unvaccinated or only partial vaccinated subjects although the effectiveness was not very high.…”

“…Moreover, household contacts had a higher SAI risk than non-household contacts. SAI incidence was 15.8% among household contacts, which was not consistent with the incidence of SAI in Denmark in a published study ( 21 ). This may be because the local government in Shenzhen immediately compulsorily isolated household contacts at designated facilities after the index cases were diagnosed, resulting in a relatively low secondary attack rate compared with published study in Denmark ( 21 ).…”

“…The secondary attack rate ( 7 , 20 ) was estimated by dividing the number of individuals with secondary infections by the overall number of close contacts related to index cases. Moreover, we analyzed the proportion of cases of supercritical transmission (SCT), which referred to cases with an individual transmission number ≥1 ( 21 , 22 ).…”

Transmission Characteristics and Inactivated Vaccine Effectiveness Against Transmission of SARS-CoV-2 Omicron BA.5 Variants in Urumqi, China

“…Individuals with infections who were associated with zero secondary infections and the close contacts of these individuals were excluded from estimating the secondary attack rate. We also considered the individual reproduction number, defined as the expected number of infections spread by 1 individual with an infection, by calculating the mean number of secondary infections associated with primary infections . The proportion of supercritical transmission is defined by the ratio at which the individual reproduction number is greater than 1, and this was measured by the proportion of individuals who spread infections who were associated with more than 1 offspring infection.…”

Replicating superspreader dynamics with compartmental models

“…Following this, the negative binomial model has been widely adopted as the canonical model for analyzing heterogeneous transmission data, although several alternatives have been proposed (e.g., see Refs. 12 , 13 ).…”