Medics first discovered noroviruses in 1972 using an electron microscope. Since then, they've found a large variety of different noroviruses, several of which are contagious to humans.

Where are they?

Noroviruses can be found all over the world. They're responsible for roughly half of all non-bacterial cases of diarrhea. Children under five as well as the weak and elderly are most vulnerable. That's why epidemic waves of infections often hit child daycares or senior living facilities. There's a risk of infection anywhere that people are confined to a space over a long period of time. At theAthletic World Championships in London, for example, there's an ongoing epidemic. And in 2012, there was a case in Germany where a medium-sized cruise ship had to be put under quarantine in Wiesbaden after 67 tourists fell ill, or roughly every second guest.

Where does the virus come from?

Noroviruses always develop inside the human: They multiply in the gastrointestinal tract and get distributed by droplet and contact infection – through the stool or the vomit. The smallest traces are sufficient to infect a healthy person: 10 to 100 virus particles are enough. Touching a slightly soiled door handle after using the toilet and then eating something out of the hand may already get you seriously sick after an incubation time of only six to fifty hours.

Can food infect me?

A norovirus can hang around in a given environment for quite some time. That's one way it gets back, via the food chain, into the human stomach. Fruits and vegetables can carry a virus, for example, if feces were used as a fertilizer - or if the agricultural workers failed to wash their hands properly before picking and collecting the fruit. Another culprit: shellfish from areas where untreated wastewater flows into rivers, lagoons or seas. Finally, drinking water can also be a problem if freshwater pipes run in close proximity to wastewater pipes; if frequent water cuts occur and the pressure in the drinking water pipe drops, contaminated water may get in. The same can occur if a cesspool is located too close to a drinking water well.

How long is an infected person contagious?

The greatest danger for others is during the time that the sickness breaks out (diarrhea and vomiting) but also for up to two days after the symptoms have stopped entirely. After that, the virus can still be excreted for another two weeks or more. During that time, anyone in contact with the infected individual should strictly follow the rules of good hygiene.

How can I treat the infection?

There isn't much doctors can do. If the patient has lost a lot of liquid, it may be necessary to give infusions, especially with small children and the elderly. There is, however, no medication against noroviruses. Patients have to be isolated as best as possible to prevent contagions. And caretakers must take extra precautions.

How can I protect myself?

No vaccine exists that protects against noroviruses. The only thing that helps is washing and disinfecting your hands or the door handles and other surfaces you come in contact with regularly; this includes keyboards, remote controls, toilets, etc. When caretakers are in contact with infected individuals they should wear rubber gloves, a surgical mask and a smock. Laundry should be washed hot. As far as food is concerned, peel fruits and cook the vegetables. And there is one more thing that certainly doesn't hurt: Try consuming lots of lemon juice. While the final scientific proof isn't there yet, there's at least good evidence to suggest that it helps!