(IDEX Online) - Three major diamond factories in Surat were ordered to close yesterday for at least 10 days, after a total of 22 of their employees tested positive for coronavirus.Municipal authorities fear packets of rough diamonds may have been the source of the infection and are urging owners to have them sanitized before they are given to the workers for polishing.The city's deputy health commissioner Dr Ashish Naik told The Indian Express news website: "Our teams had found 13 positive cases from Dharmanandan Diamonds, five positive cases from Shivam Exports and four from J & B brothers. We have slapped closure notices on all the three firms."Almost a quarter of the 3,018 Covid-19 cases reported in Surat so far have been from Katargam zone, a key diamond area. On Saturday, 77 cases were reported from Surat city, of which 26 were from Katargam.Surat Municipal Commissioner Banchhanidhi Pani said it was important to issue closure notices to the three big factories, as a warning to others that they must follow COVID-19 rules.Generic picture of Surat diamond workers