The announcement of her resignation came a day after she testified before the House Intelligence Committee on allegations related to the Russian interference during the 2016 presidential campaign.
The diagnosis comes a month after United States President Donald Trump and other members of his family and inner circle tested positive
McEnany, 32, has become the highest-ranking White House official to be tested positive for COVID-19 after President Trump and the first lady tested positive for the deadly virus that has so far killed more than 200,000 Americans this year.
The development is likely to bring to standstill Trump's hectic election campaign.
Tom Bossert's resignation came a day after John Bolton took over the role of National Security Adviser.
In a message to Trump, Xi, 67, said that after learning US President Trump and Melania have tested positive for COVID-19, he and his wife Peng Liyuan extend sympathy to them and wish them a speedy recovery, state-run Xinhua news agency reported.
According to the top US daily, Lewandowski was seen as someone having hostile relationship with members of the national press.
Sharing her experience, Melania said that she was very fortunate as her diagnosis came with minimal symptoms, though they hit her all at once and it seemed to be a roller coaster of symptoms in the days after.
Two United States Senators, a former adviser to US President Donald Trump, his campaign manager and three White House journalists have tested positive for COVID-19, joining several officials working at the presidential palace to have contracted the infection.
Russian President Vladimir Putin described Trump as a "talented and outstanding man".
The daughter of Indian immigrants from Punjab, Haley was the first woman tapped by Trump for a top-level administration post during his transition to the White House.