Researchers work at a laboratory of the disease prevention and control center in Nanyang, central China's Henan Province, Feb. 4, 2020. Photo: Xinhua

Two unusual COVID-19 cases were reported in Xinxian county in Central China's Henan Province on Sunday, which shows strong contagiosity and whose sources of infection could not be determined.The county has announced it will prolong the quarantine period for people who had been to Wuhan or contacted with Wuhan residents from 14 days to 21 days after discovering the two cases.One of the two patients, surnamed Wu, was confirmed to have been infected 34 days after returning from Wuhan, Hubei Province. Wu returned to Xinxian on January 14 and went to hospital on January 28. Wu took three nucleic acid tests before being diagnosed.During this period, Wu attended two family dinner parties and came into contact with 10 people, two of whom have been confirmed to be infected and another three are suspected of being infected.The other patient, surnamed Ning, was confirmed to be infected 94 days after coming into contact with his father-in-law, surnamed Zhang, who had been to a Wuhan hospital for medical treatment.Ning began to live with and take care of Zhang on November 13, then moved back to his own home on January 31 after Zhang passed away.Zhang only left his home three times to go to the supermarket and pharmacy until going to the hospital on January 14.