Abstract
Norovirus, the most commonly identified cause of both sporadic cases and outbreaks of infectious diarrhoea in developed countries, exhibits a complex epidemiology and has a strong wintertime seasonality. Viral populations are dynamic and evolve under positive selection pressure.MethodsTime series-adapted Poisson regression models were fitted to daily counts of laboratory reports of norovirus in England and Wales from 1993 to 2006.FindingsInverse linear associations with daily temperature over the previous seven weeks (rate ratio (RR) = 0.85; 95% CI: 0.83 to 0.86 for every 1°C increase) and relative humidity over the previous five weeks (RR = 0.980; 95% CI: 0.973 to 0.987 for every 1% increase) were found, with temperature having a greater overall effect. The emergence of new norovirus variants (RR = 1.16; 95% CI: 1.10 to 1.22) and low population immunity were also associated with heightened norovirus activity. Temperature and humidity, which may be localised, had highly consistent effects in each region of England and Wales.ConclusionsThese results point to a complex interplay between host, viral and climatic factors driving norovirus epidemic patterns. Increases in norovirus are associated with cold, dry temperature, low population immunity and the emergence of novel genogroup 2 type 4 antigenic variants.
Highlights
Noroviruses are the most commonly identified cause of acute gastroenteritis amongst both sporadic community cases and outbreaks.[1,2] Noroviruses are single stranded RNA viruses and members of the Caliciviridae family
These results point to a complex interplay between host, viral and climatic factors driving norovirus epidemic patterns
Increases in norovirus are associated with cold, dry temperature, low population immunity and the emergence of novel genogroup 2 type 4 antigenic variants
Summary
Noroviruses are the most commonly identified cause of acute gastroenteritis amongst both sporadic community cases and outbreaks.[1,2] Noroviruses are single stranded RNA viruses and members of the Caliciviridae family. There are two main genogroup of viruses causing disease in humans, with substantial genetic diversity between and within genogroups. Norovirus gastroenteritis tends to be short-lived and resolves without medical intervention in otherwise healthy individuals, evidence suggest that infections may be more severe in vulnerable populations.[3] In industrialised countries, outbreaks frequently occur in healthcare settings,[4] where economic impact may be substantial and associated deaths may occur amongst the elderly.[5] In developing countries, malnourished children or those without access to effective healthcare may suffer substantial morbidity and mortality to norovirus,[6] though this burden is yet to be accurately quantified
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