NEW YORK (Reuters) – A top U.S. health official cautioned on Thursday that protests sweeping across the country could increase the spread of the novel coronavirus, particularly in cities that have struggled to control the outbreak, and that participants should “highly consider” getting tested.

Huge crowds have taken to the streets of dozens of cities since the death of George Floyd in Minneapolis police custody set off unrest that has roiled America in the midst of the coronavirus pandemic.

Protests have occurred in Minneapolis and Washington, D.C., where there has been significant transmission of the virus, Robert Redfield, director for the Centers for Disease Control and Prevention (CDC), testified before a Congressional committee.

“Those individuals that have partaken in these peaceful protests or have been out protesting, and particularly if they’re in metropolitan areas that really haven’t controlled the outbreak…we really want those individuals to highly consider being evaluated and get tested,” Redfield told a U.S. House of Representatives subcommittee.

“I do think there is a potential unfortunately for this to be a seeding event,” he said, referring to spreading the virus.

Other public health experts and government officials have also warned the large street protests could cause a spike in new coronavirus cases.

Concerns that a second wave of the virus could also spill over into flu season in the fall have heightened fears of the potential pressure on the nation’s healthcare system.

The CDC is seeking emergency use authorization for a test to detect and differentiate flu from COVID-19, Redfield said in prepared testimony for the House subcommittee on Labor, Health and Human Services, Education, and Related Agencies.

Redfield said in the prepared testimony the CDC is working with drugmakers to maximize the availability of influenza vaccines, and with healthcare providers “to develop contingency plans so that people can be vaccinated in a safe environment.”

Major flu vaccine makers include British-based GlaxoSmithKline, France’s Sanofi and Australia’s CSL.

U.S. pharmacy chains have been preparing a big push for flu vaccinations in October, hoping to prevent tens of thousands of serious cases that could flood hospitals along with new COVID-19 cases.

Redfield also said the World Health Organization (WHO) continues to be a “close colleague” in public health efforts.

President Donald Trump said on Friday the United States will end its relationship with the WHO over the body’s handling of the coronavirus pandemic.

During Redfield’s appearance, Democrats criticized the Trump administration’s response to the outbreak, which has led to more than 107,000 U.S. deaths.

“I have such admiration for the work that you and the CDC do, but if you and the CDC are driving this bus, you’re taking us in a dangerous direction,” said Rosa DeLauro, a Democratic congresswoman from Connecticut.

Asked about the delay in widely available coronavirus testing long into the U.S. outbreak, Redfield pointed to corporate America.

“It took unfortunately weeks and weeks and weeks before the private sector stepped up and developed what we now have,” he told the panel, noting that more than 17 million coronavirus tests have now been done in the United States.