The US Centers for Disease Control and Prevention (CDC) has advised elderly and unwell Americans to avoid crowds in order to limit the impact of the coronavirus – but the White House said it was “business as usual” as the 73-year-old Donald Trump attended a fundraising event in Florida.

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The president played down the threat of Covid-19, saying many more people had died of the flu in the US than have been reported killed by coronavirus – despite warnings from his own officials that, unlike flu, the current outbreak concerns a new virus for which there is no vaccine and no natural immunity in the population. Covid-19 has also only just begun to spread in the US.

Nancy Messonnier, head of the CDC’s National Center for Immunization and Respiratory Diseases, said more than 500 cases of the virus had been reported in 34 states and Washington DC as of Sunday night. Nineteen people had died, according to the CDC, 18 of them in Washington state with the other fatality in California.

According to the World Health Organization, about 106,000 cases and around 3,500 deaths have been confirmed worldwide.

“This seems to be a disease that affects adults and most seriously older adults,” Messonnier said. “Starting at age 60, there is an increasing risk of disease, and the risk increases with age.

While we have asked all Americans to exercise commonsense hygiene measures, we are conducting business as usual Stephanie Grisham

“The data really says that as you get older, the risk goes up and so in the broader age category of over 60 or over 65, over-80-year-olds have the greatest risk and so I would recommend that people make their own decisions based on an understanding of that risk.”

Messonnier said for the elderly, or those who have an underlying disease, “we are recommending avoiding crowds because those are places where in general, there’s lots of transmission of respiratory diseases”.

Despite reports of an attendee at the recent Conservative Political Action Conference (CPAC) near Washington falling sick with coronavirus after interacting with senior Republicans including the Texas senator Ted Cruz – who placed himself in quarantine – the White House denied reports that the nation’s top officials would change their routine.

“Reports that the White House has issued formal guidelines to staff instructing them to limit in-person interactions and meetings are completely false,” said Stephanie Grisham, Trump’s White House press secretary.

“While we have asked all Americans to exercise commonsense hygiene measures, we are conducting business as usual. I want to remind the media once again to be responsible with all reporting.”

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Trump attended CPAC, where he was pictured shaking hands with organiser Matt Schlapp, who said he had contact with the infected individual early in the conference.

The Georgia Republican congressman Doug Collins followed Paul Gosar of Arizona in announcing that he was also self-quarantining, after it emerged he had been in contact with the infected person at CPAC.

Collins accompanied Trump in a tour of CDC headquarters in Atlanta on Friday.

A second congressman who had been in contact with the Covid-19 patient at CPAC, Matt Gaetz, said he would self-quarantine. Gaetz partied with Trump in the president’s Mar-a-Lago resort over the weekend and flew back with him to Washington. According to the New York Times, the congressman found out he had had contact with a coronavirus patient when he was already on Air Force One with Trump and he went to a separate part of the plane to sit alone.

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On Monday Trump spent the day in Florida, where he attended a fundraising meeting in a private residence.

Aides said 300 supporters would attend, expecting to raise $4m for Trump’s re-election campaign. Handshakes and selfies are customary for those attending such events, and Trump was pictured shaking hands with well-wishers along the way.

The White House told reporters traveling with Trump that he was not worried about contracting or spreading coronavirus, which experts say can be spread via coughs or sneezes and by physical contact.

Jeremy Konyndyk, who as head of foreign disaster assistance led the Obama administration’s response to the Ebola outbreak in west Africa in 2014, said on Twitter: “I cannot overstate how risky it is to be exposing the president of the United States to events like this right now.”