Who takes over if the president becomes too ill to work? Who else has tested positive in the White House? And what will happen to the election?
At least 140 schools across England have been forced to partially close since the new academic year started, after reporting positive cases.
Scientists advising ministers raised concerns that workers could face discrimination based on their "positive" or "negative" status.
The US president says Boris Johnson issued a plea for ventilators in a telephone call with him.