Abstract
BackgroundNorovirus (NoV) transmission may be impacted by changes in symptom intensity. Sudden onset of vomiting, which may cause an initial period of hyper-infectiousness, often marks the beginning of symptoms. This is often followed by: a 1–3 day period of milder symptoms, environmental contamination following vomiting, and post-symptomatic shedding that may result in transmission at progressively lower rates. Existing models have not included time-varying infectiousness, though representing these features could add utility to models of NoV transmission.MethodsWe address this by comparing the fit of three models (Models 1–3) of NoV infection to household transmission data from a 2009 point-source outbreak of GII.12 norovirus in North Carolina. Model 1 is an SEIR compartmental model, modified to allow Gamma-distributed sojourn times in the latent and infectious classes, where symptomatic cases are uniformly infectious over time. Model 2 assumes infectiousness decays exponentially as a function of time since onset, while Model 3 is discontinuous, with a spike concentrating 50% of transmissibility at onset. We use Bayesian data augmentation techniques to estimate transmission parameters for each model, and compare their goodness of fit using qualitative and quantitative model comparison. We also assess the robustness of our findings to asymptomatic infections.ResultsWe find that Model 3 (initial spike in shedding) best explains the household transmission data, using both quantitative and qualitative model comparisons. We also show that these results are robust to the presence of asymptomatic infections.ConclusionsExplicitly representing explosive NoV infectiousness at onset should be considered when developing models and interventions to interrupt and prevent outbreaks of norovirus in the community. The methods presented here are generally applicable to the transmission of pathogens that exhibit large variation in transmissibility over an infection.
Highlights
A recent spike in the number and severity of Norovirus (NoV) outbreaks worldwide [1] has underscored the rising costs of NoV transmission in both public health and economic terms
Environmental contamination resulting from episodes of vomiting and diarrhea [2,4,5,7] and post-symptomatic shedding that may persist for days or weeks after symptoms have resolved [8] have been implicated in transmission
Data source In December 2009, more than 200 individuals were sickened by a GII.12 norovirus outbreak caused by contaminated oysters served at a North Carolina restaurant
Summary
A recent spike in the number and severity of Norovirus (NoV) outbreaks worldwide [1] has underscored the rising costs of NoV transmission in both public health and economic terms. [2,3,4,5]) the development of effective interventions necessitates an understanding of how each stage of infection in individual cases impacts outbreak transmission. Despite documented variation in NoV symptom intensity over time, dynamic models of norovirus transmission have typically represented infectiousness as homogeneous over the life of a typical infection The methods presented here are generally applicable to the outbreak transmission of other enteric and respiratory pathogens, where variation in symptom-severity across individuals and over time can impact transmission dynamics. Sudden onset of vomiting, which may cause an initial period of hyper-infectiousness, often marks the beginning of symptoms This is often followed by: a 1–3 day period of milder symptoms, environmental contamination following vomiting, and post-symptomatic shedding that may result in transmission at progressively lower rates. Existing models have not included time-varying infectiousness, though representing these features could add utility to models of NoV transmission
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