Demonstrators take part in a protest in Uptown neighborhood of Chicago, the United States, June 1, 2020. (Photo by Chris Dilts/Xinhua)

The infection risk is even higher when demonstrators have been arrested."Jails are crowded indoor spaces. The aggregation of protesters in jails will increase the risk for onward transmission of the virus," said Zhang Zuofeng, a professor of epidemiology.

WASHINGTON, June 2 -- As tens of thousands of demonstrators continue to take to the streets across the United States to protest the killing of George Floyd, an African American who died in police custody last week, health experts warned that mass gatherings may speed up COVID-19 transmission.

"Mass gatherings occurred in many locations across the country, resulting in close contacts and lack of social distancing. Though many demonstrators wear masks, the chances of COVID-19 infections increase tremendously," Zhang Zuofeng, professor of epidemiology and associate dean for research with the school of public health at University of California, Los Angeles, told Xinhua on Tuesday.