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Understanding the importance of contact heterogeneity and variable infectiousness in the dynamics of a large Norovirus outbreak.

Abstract

We found wide heterogeneity in infectiousness across individuals, suggestive of superspreading. Nearly 50% of individual infectiousness was concentrated in the individual's sub-camp of residence, with the remainder distributed over other sub-camps. This suggests a source-and-sink dynamic in which sub-camps with greater average infectiousness fed cases to those with a lower transmission rate. Although the per-capita transmission rate within camps was significantly greater than that between camps, the large pool of susceptible individuals across camps enabled similar numbers of secondary cases generated between vs. within camps.

Large norovirus (NoV) outbreaks are explosive in nature and vary widely in final size and duration, suggesting that superspreading combined with heterogeneous contact may explain these dynamics. Modeling tools that can capture heterogeneity in infectiousness and contact and are important for norovirus outbreak prevention and control, yet they remain limited.

The consideration of clustered transmission and heterogeneous infectiousness are important for understanding NoV transmission dynamics. Models including these mechanisms may be useful for providing early warning and guiding outbreak response.

Data from a large norovirus outbreak in a Dutch scout jamboree, which resulted in illness among 326 (of 4,500 total), individuals from 7 separate camps were used to examine the contributions of individual variation in infectiousness and clustered contact patterns to the transmission dynamics. A Bayesian hierarchical model of heterogeneous, clustered outbreak transmission was applied to represent: 1) between-individual heterogeneity in infectiousness and 2) heterogeneous patterns of contact.

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