Air cooling systems used at abattoirs could be an overlooked risk factor accounting for Covid-19 outbreaks, according to scientists who have studied conditions at a meat-processing plant at the heart of a cluster of infections in Germany. Martin Exner, a hygiene and public health expert at the University of Bonn, spent two days analysing the Tönnies plant in Gütersloh, a western German city sent back into lockdown this week after around 1,500 employees were infected with coronavirus. At a press conference, Exner said the air filtration system in the slaughter area had contributed to the spread of aerosol droplets laden with the virus, describing it as a “newly recognised risk factor”. The area of the plant where animals are slaughtered, gutted and cut to pieces is kept at a cool 6-10C degrees. To do this, the cooling system circulated the same unfiltered air, thus keeping aerosols in motion, Exner said. A filter fitted to the cooling system was not able to keep out the virus, his analysis found. The findings would have “big consequences” for other abattoirs as well, Exner said. Slaughterhouses have also been at the heart of Covid-19 outbreaks in America, France, Spain, the Netherlands, Australia, Brazil and other German regions. Around 640,000 people in two neighbouring districts have also been affected by newly enforced “soft lockdown” measures. Schools and nurseries have closed down and bars, cinemas and fitness studios have had to shut their doors. Around 7,000 employees at the abattoir have been asked to self-quarantine. A “contact ban” allowing only meetings of two people from different households has been been re-established, while locals are advised to stay at home at the start of the summer holidays, which start in the region on Monday. Three northern German states, Lower Saxony, Schleswig-Holstein and Mecklenburg-Vorpommern, have said tourists from the affected districts will not be allowed to holiday in their regions, with hotels and holiday home providers instructed to cancel bookings if necessary. Austria, meanwhile, has issued a ban on non-essential travel to and from the state of North Rhine-Westphalia. Armin Laschet, the premier of Germany’s most populous state, has warned against vilifying people from the region affected by the second lockdown. “One thing simply won’t do and that is the stigmatisation of people from Gütersloh,” said Laschet, who is one of the three official candidates vying for the leadership of Angela Merkel’s Christian Democratic Union.