The Robert Koch Institute for disease control said in its daily bulletin that its estimate of the effective reproduction number, or R, had risen to 1.1.
If accurate, it would suggest that the number of infections is now growing rather than falling – raising concerns that the outbreak could again spiral out of control.
Last month, before Germany began lifting its Covid-19 restrictions on 20 April, the estimate of R was 0.7. This had increased to 0.96 by the middle of last week.
However the institute said there was a ”degree of uncertainty” around the value of R, which refers to the number of people that a sick person infects.
“It is too early to infer whether the number of new infections will continue to decrease as in passing weeks or increase again,” it said.
“The increase of the reproduction number R necessitates a close monitoring of the situation in the coming days.”
Germany has seen regional spikes in cases linked to slaughterhouses and nursing homes and on Saturday there were more than 1,250 new confirmed cases. Before the lockdown was eased the number of daily cases had fallen below 1,000.
It followed last week’s decision by chancellor Angela Merkel and the governors of Germany’s 16 states to allow restaurants, hotels and shops to reopen.
More students will return to school tomorrow, while the country’s football league resumes next week, despite a number of professional players testing positive for Covid-19.
Karl Lauterbach, a Social Democrat lawmaker and professor of epidemiology, warned that the new coronavirus could start spreading again quickly after seeing large crowds out and about on Saturday in his home city of Cologne.
“It has to be expected that the R rate will go over 1 and we will return to exponential growth,” Lauterbach said in a tweet. “The loosening measures were far too poorly prepared.”
The threshold for reimposing social distancing measures by regional authorities has been set at 50 cases per 100,000 people. It has already been triggered in two districts in the states of North Rhine-Westphalia and Schleswig Holstein, where Covid-19 broke out among workers at meat processing plants.
However Germany has so far seen far fewer deaths than Italy, France and the UK, possibly because of its high levels of testing.
On Sunday the Robert Koch Institute reported an increase of 667 confirmed cases, bringing the total to 169,218, and a rise of 26 in the death toll to 7,395.
Additional reporting by agencies
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