Factors driving transmission of norovirus outbreaks in LTCFs: a case-level analysis of 107 outbreaks Open Access

Abstract

Background Norovirus is the most common cause of gastroenteritis outbreaks in long-term care facilities (LTCFs) in the United States, causing high disease burdens in both residents and staff. Understanding how individual case symptoms and characteristics contribute to norovirus transmission can lead to more informed control measures in LTCFs.   

Methods We examined line lists for 107 norovirus outbreaks that took place in US LTCFs in six states from 2015 to 2019. We estimated the individual effective reproduction number, REi, to quantify individual case infectiousness and examined the contribution of vomiting, diarrhea, and residents (vs. staff) to case infectiousness. Individual estimations of REi were calculated by a maximum likelihood procedure that uses information on symptom onset dates and the serial interval distribution of norovirus to infer who infected whom. The associations between case characteristics and REi were estimated using a multivariate, mixed log-linear model with inverse variance weighting.

Results Vomiters infected 1.28 (95% CI: 1.11, 1.48) times the number of secondary cases compared to non-vomiters and LTCF residents infected 1.31 (95% CI: 1.15, 1.50) times the number of secondary cases compared to staff. There was no difference in infectiousness between cases with and without diarrhea (1.07 (95% CI: 0.90, 1.29)).

Conclusion Individuals who vomit, particularly LTCF residents, are more infectious than those who do not vomit and tend to drive norovirus transmission in US LTCF outbreaks.

Table of Contents

Background..................................................................................................................1

Methods………………………………………………………………………………………………………..3

Data Source…………………………………………………………………………………………………...3

Estimation of Individual Effective Reproduction Numbers, REi…………………………………..4

Analysis of Risk Factors for Transmission by Modeling…………………………………………….6

Results…………………………………………………………………………………………………………8

Outbreak Characteristics…………………………………………………………………………………8

Outbreak Transmission Patterns……………………………………………………………………….8

Risk Factors for Norovirus Transmission in LTCFs…………………………………………………10

Discussion……………………………………………………………………………………………………..12

Conclusions……………………………………………………………………………………………………15

Tables & Figures……………………………………………………………………………………………..16

Table 1……………………………………………………………………………………………………….16

Figure 1..…………………………………………………………………………………………………….17

Figure 2………………………………………………………………………………………………………18

Table 2……………………………………………………………………………………………………….19

Figure 3………………………………………………………………………………………………………20

 

Reference ………………………………………………………………………………………………………21

About this Master's Thesis

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School	Rollins School of Public Health
Department	Epidemiology
Subfield / Discipline	Epidemiology - MPH & MSPH
Degree	M.P.H.
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health Health Sciences, Epidemiology
Keyword	Norovirus Outbreaks Risk Factors Transmission Dynamics Long-Term Care Facilities
Committee Chair / Thesis Advisor	Lopman, Benjamin, Emory University
Partnering Agencies	Emory University schools, faculty or affiliated programs

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