Hours after Prime Minister Boris Johnson revealed on Friday he had the coronavirus, his health minister said he did too, and England's chief medical officer announced he also had symptoms.

There can be no way to know if they infected each other or caught the illness from another person, or different people. But the three men had met a handful of times in person over the previous 10 days, according to Johnson's official diary, to formulate Britain's response to the outbreak.

On Tuesday of last week, when most ministers video-conferenced into a cabinet meeting, Health Secretary Matt Hancock and chief medical officer Chris Whitty sat in the room with Johnson. Whitty had also stood alongside the prime minister at three of the 11 news conferences on the coronavirus since March 16.

Now the question on the lips of many at Downing Street and beyond is: How many other people did the UK prime minister come into contact with before testing positive?

Asked about whether those who became ill believed they had done so from meeting Johnson, a government source noted that scientists say it takes around five days from transmission to developing symptoms so people who became ill at the same time "almost certainly" did not give it to one another.

Johnson is the first world leader to announce he is sick with COVID-19, the respiratory disease caused by the novel coronavirus. But other administrations have faced similar questions.

German Chancellor Angela Merkel, Brazilian President Jair Bolsonaro and U.S. President Donald Trump say they have tested negative for coronavirus, while Canadian Prime Minister Justin Trudeau went into self-isolation earlier this month after his wife tested positive.

Michel Barnier, the European Union's chief Brexit negotiator, has tested positive, as have several members of the U.S. Congress.

For politicians, who can meet hundreds of people every day, the coronavirus crisis requires a balance between being seen to lead their people while also keeping a safe distance.

Johnson's spokesman, asked repeatedly about the prime minister's contacts with other people, told reporters on Friday the prime minister had not been in close proximity with anyone "from the moment he had symptoms."

According to Johnson's statement, that would mean Thursday of last week. And according to his public agenda, Johnson had scaled back in-person meetings, in accordance with the UK's wider lockdown rules, from Monday March 23.

Face-to-face meetings

Yet scientists say the virus' incubation period is estimated at between one and 14 days, and there have been anecdotal accounts of people spreading the disease without having symptoms.

And despite the scaling back, Johnson still met Whitty in person or via videolink at least eight times in the last two weeks and Hancock around nine, according to his diary, to plot Britain's response to the coronavirus outbreak.

Meetings were also held with other staff, according to two sources close to the prime minister. One Downing Street source said that 75 of the 200 staff who usually work at Number 10 – an approximately 100-room town house – are still working there in separate rather than overlapping shifts to reduce the risk of infection.

Johnson also had regular in-person news conferences with journalists at Downing Street until March 24, when he switched to ones where the journalists attended by video link. Some journalists who attended the in-person conferences have said via social media or have told colleagues that they are now self-isolating.

"Here in Number 10 we have been observing the advice ... we have wherever possible been using video conferencing, you'll have seen the prime minister ensuring he is a safe distance from colleagues when he is taking part in press conferences," Johnson's spokesman said on Friday.

The prime minister also ventured beyond Downing Street last week. On Wednesday, a day before his positive test, Johnson answered questions at a weekly session in parliament's House of Commons chamber.

In the live video, Johnson is seen speaking with several lawmakers. Minister for Scotland Alister Jack, who sat next to Johnson before the session, said on Saturday he had developed a temperature and a cough and was now working from home in isolation.

Asked whether Jack believed suggestions he may have become ill in parliament that day, the Office of the Secretary of State for Scotland declined to comment, saying it had nothing to add to Saturday's statement.

Distancing

At first, Britain's response to the spread of the virus was not as stringent as in other countries. It was only at the beginning of the week from March 16 that the UK position began changing – and Johnson's rhythm too.

In addition to more video-conferences, audiences with Queen Elizabeth – usually held weekly – have been held by telephone for the last two weeks, according to Johnson's spokesman.

Schools across the UK were closed from March 20, and the prime minister announced three days later that all shops – except for the most essential ones – would be closed.

On Friday, just five hours after Johnson said he had tested positive for coronavirus, Whitty wrote on Twitter that "after experiencing symptoms compatible with COVID-19 last night ... I will be self-isolating at home for the next seven days." He said he would continue to advise the government.

The same day, Hancock said he had also tested positive and was self-isolating at home with mild symptoms. He has since been active on Twitter, but has not commented on his condition.

The health ministry said on Sunday it could offer no update on the conditions of Hancock or Whitty.

Apart from Hancock and Whitty, the other person who has spent the most time working on the British government's response is the government's chief scientific adviser, Patrick Vallance.

Whitty, Johnson and Vallance were seen so often at news conferences together in the second and third weeks of March that they were called the "three amigos" in reference to a 1986 comedy with Steve Martin.

After Johnson made his announcement, Vallance tweeted that he had no symptoms. Vallance could not be reached for comment.