Why is nucleic acid everywhere in Hanzhong today?

According to the Regulations on Epidemic Prevention and Control in Hanzhong City, as of September 15, 2022, due to the epidemic situation, all staff in Hanzhong City need to carry out nucleic acid testing. Hanzhong, referred to as Han, is a prefecture-level city under the jurisdiction of Shaanxi Province. Arrive in Hanzhong, test nucleic acid for 48 hours, show green health code and travel code, and wear a mask all the time.