Noroviral infection (also known as as winter vomiting bug) is a feature of the medical landscape every winter.
Every half dozen years or so however, we encounter "upsurge years", characterised by unusually marked increases in norovirus notifications and outbreaks (especially in the acute and residential health sectors). The last major global upsurge year was in 2012, originating in Sydney, Australia. The strain responsible (the "Sydney 2012" strain) belongs to norovirus Genogroup II; the dominant strain of norovirus detected worldwide and in Ireland since 2002.
In September 2016, researchers in Australia identified novel norovirus strains (which had evolved from the Sydney 2012 variant) that produced extensive winter illness in Australia. The emergence of these new strains explains the increased levels of norovirus now being reported. The reason behind these upsurges is the level of population immunity to norovirus. Immunity to norovirus is partial and temporary, lasting only a matter of months. This feature of temporary immunity, coupled with the slow evolution of the virus, accounts for the waxing and waning of activity, characteristic of the epidemiology of this virus.
In the last five weeks (until 19/12/2016), we have seen a tripling in the numbers of weekly norovirus notifications reported to HPSC (from 29 to 97 cases). This heightened norovirus activity is mirrored across Europe and North America, providing additional confirmation that we are entering a period of generalised upsurge.
In the past, when upsurge periods such as these have commenced in the final weeks of the year, they are typically sustained for about 8-12 weeks. In other words, we can expect this level of heightened norovirus activity to continue until at least the end of February 2017.
Norovirus is an unpleasant but largely mild illness. Its significance lies in its high infectiousness and extreme transmissibility. A person with noroviral illness will excrete as many as 50 million virus particles with each episode of vomiting - it takes fewer than 10 virus particles to make a healthy individual sick. This underlines the need to minimise the possibility of introduction of the virus into the acute sector.
For the health system: We are entering a upsurge period for norovirus activity. There are increasing levels of norovirus circulating in the community. Accordingly, there is heightened risk of norovirus being introduced into hospitals and residential facilities (by both staff and the general public) with all the attendant knock-on effects of norovirus outbreaks in such settings, namely ward closures, OPD delays and cancellations, postponed operations, and, the potential for severe disease in vulnerable in-patients already weakened by other co-morbidities.
For directors of public health: I would be grateful if you could bring this information to the attention of Nursing Homes/Residential Facilities and General Practitioners in your area.
The HPSC website has extensive resources on norovirus:
A guidance document, National Guidelines On The Management Of Outbreaks Of Norovirus Infection In Healthcare Settings from 2003 is still current and gives step-by-step instructions on management of norovirus in healthcare settings.
In addition, a press release, to bring the current upsurge of norovirus to public attention, is being prepared for release shortly. This will highlight the importance to the general public, of not attending/visiting hospitals or nursing homes if unwell with vomiting and diarrhoea, to minimise the risk of introduction of norovirus into the acute and residential sectors. It is crucial to get this message across at a time of year when the acute system is under stress, particularly from respiratory viral illness.
Instead, ill members of the general public are being advised to telephone their GP (rather than attend the surgery), again, to minimise the risk of introduction of infection into the surgery. Alternatively, ill members of the public can seek advice from their local pharmacist. Relevant information is available on the HPSC website for healthcare staff and the general public.
Each week, on Wednesday, HPSC releases by email its Weekly Outbreak Report to the system. Through this report, we will keep the system updated on the current levels of circulating norovirus to ensure you are informed of the ongoing level of norovirus activity and early signs, once they begin to appear, that the upsurge is declining.
Health Protection Surveillance Centre (19 December 2016)
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