More than 300 people fell ill with gastrointestinal complaints after visiting a spring folk festival in the south-western German city of Stuttgart, the city reported on Wednesday.
All those affected had visited the same festival tent and afterwards complained of vomiting, nausea and diarrhoea, with the city describing the incident as a major outbreak.
The operator of the tent in question did not immediately comment.
The symptoms suggest a viral illness, according to the city, with increasing indications that it was a norovirus. Among those affected were both visitors to the festival and employees of the affected tent.
The food control and health authorities were on site immediately after the first reports arrived and checked the hygiene in the tent and took samples of the food.
These are currently being analysed in the laboratory, according to the city. The main task now is to contain the outbreak and find the source of the infections, with the focus on the central service areas of the tent.
Noroviruses cause nausea, vomiting and diarrhoea, and are very contagious and spread rapidly, especially in places where many people come together, such as nurseries, old people's homes or hospitals.
An infection is usually short and severe. Those affected feel weak, often have abdominal pain, headaches and aching limbs, and sometimes a slight fever.
The 84th Stuttgart Spring Festival began on Saturday with the traditional tapping of a beer keg. The festival lasts for 23 days and includes amusement rides, vendor stalls, snack bars and festival tents for music, beer and other drinks.
Organizers expect at least 1 million visitors to attend the festival, after more than 1.4 million people attended last year's event.