Stuttgart (Germany): Over 800 people have been affected by a norovirus outbreak at a festival in south-west Germany, media reports said.

The infection causes vomiting, diarrhoea, nausea, and in some cases high fever, body ache, and headache.

According to a BBC report, people attending the festival caught the bug in a marquee at the Stuttgart spring festival last weekend.

It is still unclear how the virus was first contracted, but cases of infection have risen during the week.

Meanwhile, Stuttgart officials are certain that the infections was not linked to food or drink made available in the festival tent all the samples had tested negative.

The city's health department conducted tests on marquee staff, dishes, and water used for washing them up.  They think that the virus was transmitted from person to person, potentially through the air, although the original source, whether a visitor or an employee, remains unclear.

The symptoms of the infection showed immediately as people quickly complained of vomiting, nausea and diarrhoea.

By Friday afternoon, Stuttgart health officials said the number of people infected had reached 815.

The spring festival, situated on the banks of the Neckar River, started last Saturday and will continue for 23 days till May, with a range of rides, stalls, snack bars, and marquees providing refreshments and entertainment.

It recorded a footfall of 1.4 million visitors last year.

The operator of the Göckelesmaier marquee Karl Maier told German media that "someone apparently brought norovirus in on Saturday evening” to the tent, said the BBC report.

Stuttgart health authorities confirmed that there is no proof of hygiene regulations being violated.

The Göckelesmaier marquee was thoroughly disinfected after the previous weekend and has now recommenced operations.

According to city spokesman Sven Matis, there are growing signs that the virus transmission began in the main serving area before spreading throughout the entire marquee, reported BBC.

It is believed that most of the people became ill after visiting the tent, with some of the infected people being staff members.

Officials said the possibility that certain visitors might have transmitted the virus through secondary infection.