Epidemiology and Infection

Gastrointestinal infection

Risk factors for symptomatic and asymptomatic norovirus infection in the community

G. PHILLIPSa1 c1, C. C. TAMa1, L. C. RODRIGUESa1 and B. LOPMANa1

a1 Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK


The objective of this study was to investigate risk factors for norovirus-associated infectious intestinal disease (IID) and asymptomatic norovirus infection. Individuals with IID and healthy controls were recruited in a community-based study in England (1993–1996). This is the first risk-factor study to use viral load measurements, generated by real-time RT–PCR, to identify cases of norovirus-associated IID and asymptomatic infections. Using multivariable logistic regression the main risk factor identified for norovirus-associated IID was contact with a person with IID symptoms. Infectious contacts accounted for 54% of norovirus cases in young children and 39% of norovirus cases in older children and adults. For young children, contacts outside the household presented the highest risk; for older children and adults, the highest risk was associated with child contacts inside the household. Foreign travel and consumption of shellfish increased the risk of norovirus-associated IID. Lifestyle and dietary factors were associated with a decreased risk of both norovirus-associated IID and asymptomatic infection. No risk factors were identified for asymptomatic norovirus infection.

(Accepted November 10 2010)

(Online publication December 17 2010)


c1 Author for correspondence: Dr G. Phillips, Institute for Health and Human Development, University of East London, Water Lane, London E15 4LZ, UK. (Email: g.phillips@uel.ac.uk)