CHICAGO, Dec. 5 (Xinhua) -- Joel Lerner living in U.S. Midwest state of Illinois did not feel well in late July. He had a sore throat and a mild fever. His doctor suggested he take a COVID-19 test. The result was positive at the beginning of August.

"I was surprised that I tested positive because I had been pretty careful regarding quarantine... being careful to mask up and wash hands," Lerner told Xinhua. But as a photographer, he needs to work outside. "Not everyone I encountered was as careful."