President Donald Trump tweeted early Friday morning that he and his wife, Melania, have tested positive for COVID-19, the illness that has killed more than 207,000 Americans and that he has tried to downplay in his public remarks. The couple will quarantine in the White House, which means he will be off the campaign trail, at least temporarily, just 32 days before the election. 

Details so far are few, although the First Lady tweeted that she and her husband were "feeling good."

Later Friday morning she added that she had mild symptoms of the virus.

Here are answers to some questions you may have:

Q: Might the test results be wrong?

A: President Trump and his close associates are tested every day. In the past, he has touted the test, a rapid molecular diagnostic test made by Abbott Laboratories. While it can produce a false alarm, called a false positive, it is reasonable to assume he would have a confirmatory test before announcing he is positive.

Q: What are the president's risk factors for serious illness?

A: Although he said he was in great health after his latest physical exam, the president's age, 74, and weight, which qualifies as obese, put him at high risk.

People aged 65 and up account for about 80% of reported COVID-19 deaths. Many of them already had age-related chronic illnesses that have damaged their lungs, heart, blood vessels, and kidneys -- organs that COVID-19 can attack. The mortality rate for infected people age 70 and up is estimated to be about 5%, according to the Centers for Disease Control and Prevention.

But obesity -- defined as a Body Mass Index of 30 or more (174 pounds for a 5-foot-4 woman) -- is a risk factor that transcends age. A French study of COVID-19 patients in intensive care found those with a BMI over 35 had a sevenfold higher chance of needing mechanical ventilation than those with a BMI in the healthy range. A study of COVID-19 patients under age 60 who were hospitalized in New York City found that a BMI over 35 almost quadrupled the chance of needing critical care.

Exactly why is not clear, but the virus appears to exploit a number of weight-related abnormalities, as explained in a review of eight studies published recently in the journal Endocrinology, Diabetes and Metabolism.

Being male is also a risk factor for more serious COVID-19. White people have been at lower risk, but it's hard to know how much of that is behavioral or socioeconomic.

Q: When was he likely exposed to the virus?

A: The White House has not said, although the president announced his own positive test on Twitter hours after having tweeted that his close aide Hope Hicks had tested positive.

Q: Does the president have any symptoms?

A: Symptoms tend to develop within 2 to 12 days of being exposed, usually at about 5 days. So far, President Trump may be showing mild symptoms of the novel coronavirus, according to The New York Times. The president has had what one person described as coldlike symptoms. Another person said he seemed "lethargic" at a fund-raiser he attended at his golf club at Bedminster, New Jersey, on Thursday.

On Thursday night, a White House official said the president's treatment plan was still being discussed, as was the idea of a national address or a videotaped statement to show the president is functioning.

Q: What are the implications for the campaign?

A: The White House did not say how long Mr. Trump would have to remain isolated, but it canceled his plans to fly to Florida for a campaign rally on Friday, stripping his public schedule for the day of everything except a midday telephone call "on COVID-19 support to vulnerable seniors," according to the New York Times.

He is scheduled to appear at rallies in Wisconsin on Saturday and in Arizona on Monday. These are sure to be canceled, but it is not clear what will happen to the next debate, scheduled for Oct. 15.

Q: What is contact tracing and how will it be used in the President's case?

A: Contact tracing has been used in public health for more than a century to track and help contain the spread of infectious diseases and, according to epidemiologists, is a critical tool in controlling COVID-19.

It works like this: When someone tests positive for the infectious disease a contact tracer calls them to ask questions about where they went and who they came into contact with in the weeks leading up to their positive test. Tracers then call all the contacts named to let them know they may have been exposed to the virus and to provide instructions on how to self-quarantine.

The work is incredibly challenging because it must be done quickly to reduce the likelihood that a positive case's contacts have continued to spread the virus and because it relies on patients' willingness to share information. Information collected by tracers is considered confidential, but many people are still reluctant to speak honestly because they worry others will be angry with them for getting them sick, because they don't trust the government or, if they are undocumented, because they worry speaking out will jeopardize their safety.

The more contacts a person has had, the more complicated tracing becomes. In Trump's case, a carefully coordinated schedule makes it easy to know where he has been in recent weeks, but it may be difficult to track down everyone he came into contact with, since he encounters so many people.