The Associations between Norovirus Outbreak Transmission Mechanisms and Vehicles with Attack Rate, Genogroup Distribution, and GII.4 Strain Distribution: An Outbreak Meta-Analysis Open Access

Bitler, Elizabeth Jane (2012)

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Norovirus outbreaks are responsible for significant morbidity and mortality worldwide. Norovirus outbreaks can result from foodborne, waterborne, and environmental transmission, with commonly implicated food vehicles including shellfish, produce, and ready-to-eat (RTE) prepared foods, and commonly implicated water vehicles including tap, ground, surface, and recreational water. Attack rate, genogroup distribution, and GII.4 strain are important outbreak outcomes, and may assist in implicating a particular transmission mechanism or vehicle. The goal of this study was to assess the association between outbreak transmission mechanisms and vehicles with attack rate, genogroup distribution, and GII.4 strain distribution. We used bivariate and multivariate techniques to control for other outbreak characteristics. We observed that attack rate did not vary by transmission or food vehicles, upon controlling for other outbreak characteristics, but it did vary by water vehicle. In contrast, genogroup distribution did significantly vary by transmission and food vehicles upon controlling for other outbreak characteristics, but it did not vary by water vehicle. GII.4 strain did not vary by transmission, food vehicles, or water vehicles. We also observed other significant associations between outbreak characteristics (e.g. setting, season, and hemisphere) and outbreak outcomes. Taken together, these results suggest that attack rate may be useful for implicating water vehicles, and genogroup may be useful for implicating transmission mechanisms or food vehicles, however GII.4 strain distribution may not be useful for implicating transmission mechanisms or vehicles during an outbreak investigation. Knowledge of these relationships may help public health workers to more rapidly identify transmission mechanisms or vehicles during norovirus outbreak investigations to reduce morbidity and mortality.

Table of Contents

Chapter I: Literature Review 1
Norovirus Incidence and Prevalence 1
Historical Perspective 2
Clinical Presentation 2
Epidemiology 3
Transmission Routes and Common Vehicles 3
Attack Rate 7
Genotype 7
Additional epidemiological characteristics 10
Analysis of multi-outbreak data 12
Goal and aims 14
Public health significance 15

Chapter II: Manuscript 16
Title 16
Authors 16
Abstract 16
Introduction 18
Methods 22

IRB 22
Outbreak Data 22
Data Analysis 23

Results 24
Bivariate Analysis 24
Multivariate Analysis 25

Transmission 25
Food Vehicles 26
Water Vehicles 26
Discussion 28
Limitations and Strengths 32
Implications 33
Conclusions 34

References 35
Tables 45

Table 1 45
Table 2 46
Table 3 47
Table 4 48

Appendix A: IRB Letter of Exemption 49

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