The norovirus is in season: Why these pathogens are so dangerous


You might say the norovirus is the ninja of the virus world: stealthy and highly efficient. Ten virus particles are enough to infect a human being. This makes the virus one of the most infectious pathogens out there. Especially during the colder winter months, the number of gastrointestinal diseases caused by the virus rises rapidly.

The norovirus is considered the “perfect pathogen”: it is highly contagious and extremely resistant. A mere 10 to 100 virus particles are sufficient to cause an infection1. In addition, the virus can survive on inanimate surfaces for up to a week 2 and tolerates temperatures between -20 and 60 degrees Celsius1.

Patients suffer from nausea, abdominal pain, diarrhoea or vomiting for one to three days. Other individuals can easily become infected through smear infections. With each instance of vomiting or diarrhoea, affected patients excrete tens of billions of pathogens, which can settle on door handles, furniture or hands. Theoretically, a single infected person could trigger a local epidemic.

In August 2018, Horseshoe Lake County Park near Seattle, Washington, USA, had to be closed after health officials suspected that nearly 150 people had contracted norovirus while swimming there.

####Winter is norovirus season

This example is a prelude to the norovirus season, which usually lasts from October to March in the northern hemisphere, and from June to September in the southern hemisphere.

The Centers for Disease Control and Prevention (CDC) estimate that noroviruses cause approximately 685 million infections worldwide each year, making them the most common cause of acute gastroenteritis worldwide. The viruses are responsible for every fifth case of acute gastroenteritis, which leads to diarrhoea and vomiting. Around 200 million of those affected are children under the age of five. About 200,000 patients die from the virus every year, including about 50,000 children, mainly in low-income countries.

Since 2002, the so-called GII.4 strains (genogroup II genotype 4) have caused most norovirus outbreaks worldwide, according to the CDC. However, in recent years other strains (such as GII.17 or GII.2) have replaced the GII.4 strains as main triggers in several Asian countries.3

Studies have also shown that the vigorous spread of noroviruses in Germany in the winter of 2016/17 was associated with a new virus variant.4 In total, 40 to 50 per cent of these norovirus diseases were caused by a new virus type (GII.P16-GII.2). It has also appeared in other countries such as France, Australia, Japan and China. In the past 2017/18 season, the figures returned to an average value.

Experts estimate the cost caused by noroviruses worldwide at $60 billion. The expenses are mainly due to health care costs and productivity losses.4

Recently, researchers led by Dr. Nihal Altan-Bonnet of the National Heart, Lung, and Blood Institute (NHLBI) in Bethesda, Maryland, USA5 discovered a mechanism that could explain why the viruses are so contagious: They apparently form clusters and hide in membrane vesicles – similar to hiding in a Trojan horse – to escape the body’s own defence system.

The researchers are not yet able to predict how many infections will develop in the current 2018/2019 season. By Octobre 2018, the Robert Koch Institute had reported around 58,000 cases of norovirus infections in Germany, roughly the same level as in the year before.6 However, this figure also includes the figures from the end of the previous season. The RKI updates the figures weekly7. Cases decreased rapidly from May 2018 (see graph). Since about the end of July they have been slowly rising again. The start of the norovirus season can also be observed in media coverage. Accordingly, reports of outbreaks in health care facilities and retirement homes are also increasing.

Hand hygiene is the best prevention

Although researchers are searching intensively for a vaccine against noroviruses, there is still no preventive vaccination available. In practice, it is therefore all the more important to disinfect one’s hands regularly between patient contacts, as well as surfaces in the vicinity of the patient – as self-protection and for the benefit of the patients. The required spectrum of action is limited virucidal PLUS or virucidal. The use of an antiviral disinfectant is recommended when dealing with patients who are already ill. This prevents the virus from spreading further.

Further informationen

  1. Norovirus-Gastroenteritis, RKI guidebook (German)

  2. How long do nosocomial pathogens persist on inanimate surfaces? A systematic review, BMC infectious diseases

  3. Norovirus Worldwide, Centers for Disease Control and Prevention

  4. EpidemiologischesBulletin, 07/17, Robert Koch Institut

  5. Vesicle-Cloaked Virus Clusters Are Optimal Units for Inter-organismal Viral Transmission, Cell Host & Microbe, August 2018

  6. EpidemiologischesBulletin, 46/18, Robert Koch Institut

  7. EpidemiologischesBulletin, Robert Koch Institut

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