President Donald Trump early on Friday morning tweeted that he and first lady Melania Trump had tested positive for coronavirus (COVID-19).

The president's announcement came just hours after Bloomberg News reported that White House aide Hope Hicks had tested positive for COVID-19 and would be undergoing quarantine procedures. Hicks and Trump were in close contact for most of the week as they traveled to Ohio and Minnesota.

The president testing positive for COVID-19 means that anybody who has recently come into close contact with him is at risk as well. This includes the president's Democratic challenger, former Vice President Joe Biden, who shared a debate stage with Trump on Tuesday night. Despite observing social distancing at the debate, Trump often spoke loudly and did not wear a mask, meaning Biden and Fox News debate moderator Chris Wallace may have been exposed to infectious aerosols during the 90-minute debate.

The U.S. National Institutes of Health published research earlier this year that indicated infected aerosols from loud talking could "stay in the air for between eight and 14 minutes," as summarized by MIT Technology Review. Still, epidemiologist Eric Feigl-Ding tweeted on Friday that the risk to Biden was not necessarily high.

Unlike Biden, who has largely eschewed traditional campaign rallies, Trump has been criticized for continuing to hold large events — often with crowds of supporters going maskless and ignoring social distancing guidelines. Former Republican presidential candidate Herman Cain died earlier this year with complications from COVID-19 after attending a large Trump rally in Tulsa, OK, in June.

On Wednesday, September 30, Trump held a rally at Duluth International Airport in Minnesota, where a crowd of 3,000 gathered to hear him speak, which the president did — often loudly.

UPDATE (10/2/2020): Former Vice President Joe Biden has tweeted that he and his wife, Dr. Jill Biden, have tested negative for COVID-19.