Reconstructing household transmission dynamics to estimate the infectiousness of asymptomatic influenza virus infections

Abstract

There has long been controversy over the potential for asymptomatic cases of the influenza virus to have the capacity for onward transmission, but recognition of asymptomatic transmission of COVID-19 stimulates further research into this topic. Here, we develop a Bayesian methodology to analyze detailed data from a large cohort of 727 households and 2515 individuals in the 2009 pandemic influenza A(H1N1) outbreak in Hong Kong to characterize household transmission dynamics and to estimate the relative infectiousness of asymptomatic versus symptomatic influenza cases. The posterior probability that asymptomatic cases [36% of cases; 95% credible interval (CrI): 32%, 40%] are less infectious than symptomatic cases is 0.82, with estimated relative infectiousness 0.57 (95% CrI: 0.11, 1.54). More data are required to strengthen our understanding of the contribution of asymptomatic cases to the spread of influenza.

Keywords: asymptomatic cases; influenza; transmissibility.

Fig. 1.

Panels (A and B), Summary of estimates from the models fitted in main and alternative analysis. The point and line indicate the point estimate and the 95% credible interval of the estimate, respectively. Panels (C and D), Simulation results of the impact on estimates of relative infectiousness of asymptomatic cases (case without ARI) compared with symptomatic cases (case with ARI) under different assumptions of misclassification probabilities of symptomatic and asymptomatic cases. Points and lines indicate the mean and 2.5% and 97.5% percentiles across 200 replications. The red dotted line indicates the simulation value of the relative infectiousness parameter. Panel (E), Timelines of our study and local influenza activity for pH1N1 (red) in the study period. Brackets on top represent the period for the four rounds of sera collections (R1 to R4).