Matt Gaetz, a representative for Florida, shared a picture of himself wearing the mask on Twitter ahead of a vote on an emergency funding package for the US response to the virus last week.
On Monday, he was told to quarantine himself after learning that he came into contact with an attendee at CPAC, a major conservative conference, who tested positive for Covid-19.
“While the Congressman is not experiencing symptoms, he received testing today and expects results soon,” a statement from Mr Gaetz's office said.
Although he has insisted he was not making light of the outbreak in his Twitter post, the Republican lawmaker received widespread criticism for the image, which followed an interview with Vanity Fair that showed him joking about the virus.
As he complained about a lack of media coverage for himself due to the outbreak dominating the news cycle, Mr Gaetz said: “I am just low-key convinced that Jillian [Lane Wyant - his chief of staff] would give me coronavirus to get me back on television.”
The congressman also jokingly asked if coronavirus was being “weaponised” to “take out the boomers”.
The backlash against his response to the virus was intensified on Saturday, when it was revealed that one of his constituents, a resident from his district in Santa Rosa County, Florida, had died due to a coronavirus-related illness.
“This is an absolute tragedy. It is also deeply saddening that when presented with an opportunity to lead, @RepMattGaetz chose to make a cheap joke about an epidemic that would ultimately claim the life of one of his constituents,” Bobby L Rush, a Democratic congressman for Illinois, wrote on Twitter.
Mr Gaetz said he was “extremely saddened” to learn of the death on Saturday.
He is one of five senior Republicans, including senator Ted Cruz, who have self-quarantined over their contact with the CPAC attendee.
Doug Collins, a Georgia congressman who has gone into self-isolation, was seen greeting Mr Trump with a handshake in Atlanta on Friday when the pair visited the headquarters of the Centre for Disease Control (CDC).
Mark Meadows, the president’s newly appointed chief of staff, was also among the five self-quarantined Republicans.
Health experts have warned coronavirus is likely to spread widely in the US, which has already seen more than 700 confirmed cases and at least 26 deaths from the outbreak.
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