Norovirus, also referred to as the winter vomiting virus, Norwalk virus or small round structured virus, causes misery for around a million people every year in the UK.
It is the commonest infectious cause of both diarrhoea and vomiting, which combined are otherwise known as gastroenteritis. While most cases occur during the winter, noroviral infection may occur at any time during the year. Outbreaks often occur in communal environments, such as schools and nursing homes. Infection from this virus alone was estimated to cost the NHS around £100m in 2003.
The most common symptom caused by norovirus is vomiting, which is often projectile in nature. Diarrhoea, abdominal cramps, fever and headaches can also occur. Symptoms tend to occur 24 to 48 hours after exposure to the virus. This relatively long incubation period often makes it very difficult to trace exactly from where or from whom the virus was contracted.
TRANSMISSION
Norovirus is aerosolised when an affected person vomits. The virus will travel through the air on microscopic water droplets landing on surfaces such as toothbrushes or on a person directly. Other mechanisms of infection may occur through infected stool and contaminated water or food products.
To make matters worse, unlike some micro-organisms, the virus can survive on hard surfaces away from a human host for many days. In addition, a number of different strains of norovirus exist and immunity to one strain does not confer protection against other types. These factors, and the fact that people may develop symptoms from ingestion of as little as 50 viruses, make norovirus a highly contagious and potentially destructive infection among communities.
TREATMENT
The illness lasts around 48 hours on average, but can range from 12 to 60 hours. The main complication of norovirus, as with any form of gastroenteritis, is dehydration. Clinical signs suggestive of dehydration include headache, dry mouth, thirst, dry skin and dark concentrated urine.
In extreme cases, severe dehydration may cause sunken eyes, cold hands and feet, reduced urinary output, fast pulse and dizziness due to low blood pressure, kidney failure, seizures, heart rhythm problems and even death.
As such, it is imperative that affected people are encouraged to drink plenty. Oral rehydration therapy (ORT) is recommended over the use of plain water, as it contains salts such as sodium and potassium, which are lost in gastroenteritis patients. ORT usually comes in a sachet to be reconstituted with water and is available from most pharmacies. Some patients may require intravenous hydration, that is, fluids introduced through a canula inserted into a vein.
It is recommended that most people with norovirus should stay at home rather than see their GP and risk spreading the virus to other patients or heathcare workers. Medical advice should be sought for those with chronic illnesses such as diabetes or heart problems, diarrhoea and vomiting lasting for more than three or four days, or significant dehydration.
CARE AND SUPPORT
Children affected by norovirus should refrain from returning to school or nursery for at least 48 hours after they have recovered, to reduce the risk of spreading and possibly creating an epidemic. Public swimming pools should be avoided for at least two weeks.
It is crucial to keep to strict hygiene measures, especially thorough and frequent handwashing by both those affected and people in close proximity. Norovirus is resistant to alcohol-based hand cleansers, so soap and water should be used.
Toilets should be flushed only when the lid has been closed, to reduce the risk of aerosolisation of the virus. All surfaces should be cleaned regularly, and toothbrushes should be kept in a separate room and washed properly. Food should be prepared with particular care.
Norovirus is a highly contagious and robust virus. As it only takes a few viruses to cause symptoms and the incubation period is about two days, it has almost perfect characteristics to spread like wildfire and create epidemics. Antibiotics don't affect the virus and the best treatment is supportive, ensuring that patients maintain adequate hydration. If in doubt, always seek medical advice.
Dr Raj Thakkar BSc(Hons) MBBS MRCGP MRCP(UK) is a full-time GP in Buckinghamshire.