At least 170 doctors and patients at a hospital in central Russia have tested positive for coronavirus in preliminary tests, the state-run RIA Novosti news agency reported Friday.

The Kuvatov Republic Clinical Hospital, the main hospital in the city of Ufa, was placed under strict lockdown on Monday after at least five doctors and two patients fell ill with coronavirus symptoms. About 1,100 patients and doctors have been staying in the hospital since then.

“The initial coronavirus test was carried out in the hospital and the results were negative for most patients and doctors,” said Maxim Zabelin, health minister for the republic of Bashkortostan where Ufa is located. “One hundred and 70 of them must be tested a second time to confirm or disprove the results.”

An elderly patient who died on April 5 tested positive for coronavirus in a posthumous test.

Health experts have warned that hospitals and healthcare workers could be accelerating the spread of the deadly pandemic that has infected more than 1.6 million people worldwide. In the northern republic of Komi, a rash of infections spread across six hospitals, making it Russia’s second most infected region per 100,000 residents after Moscow.

The republic of Bashkortostan has officially reported 40 coronavirus infections. Nationwide, Russia has confirmed 11,917 cases.