“Within minutes of their diagnosis being made public, our systems began surfacing authoritative news sources on our homepage, as well as in search results and watch next panels regarding the President and Covid-19,” YouTube spokesperson Alex Joseph said in a statement.

A Facebook spokesperson, who declined to be named because the situation is “rapidly evolving”, said in an email that the company is tracking the spread of conspiracy theories and will work to fact check and label misleading content.

The company said it would also remove content that violates policy, such as calls for death and celebration and claims that the election is being cancelled or postponed.

Twitter did not outline new efforts to contain conspiracy theories around Trump’s diagnosis.

“Using a combination of technology and human review, our teams have taken steps to address coordinated attempts to spread harmful misinformation around Covid-19. This applies today too,” Twitter spokeswoman Liz Kelley said in a statement.

Taking action on content that breaks rules, including spam and content that expresses a desire for death, serious bodily harm or fatal disease is part of ongoing work to protect public conversation, she said.

Trump flown to hospital after being given experimental drug for Covid-19

Platforms have long been under fire for allowing false information and discriminatory ideologies to spread on their platforms. In recent months, they’ve been under pressure to more comprehensively tackle white supremacist content as well as Covid-19 and election-related disinformation.

Facebook has come up short in its attempts to contain QAnon content, which burst into the mainstream earlier this year.

In August, Facebook said it removed 790 QAnon groups and restricted an additional 1,950 related to the conspiracy. Since then, a QAnon Facebook group added hundreds of new followers, and the company’s own algorithm recommended users to groups discussing the theory, The New York Times found.

In July, Twitter said it was removing thousands of QAnon accounts, but many returned within weeks, according to The New York Times investigation.

Why Donald Trump’s coronavirus diagnosis ‘worst nightmare’ for his campaign

Reddit did not immediately respond to an inquiry about what type of Trump coronavirus conspiracy theories and other harmful activity has circulated on the platform.

Notably, QAnon conspiracy theories were not the only ones to question the confirmation of Trump’s positive test. In the hours following the news, many liberals question whether they were being misled, suggesting it could be a ploy as polls show Trump trailing Democratic nominee Joe Biden in polls, one month before November’s election.

“Here’s how wrecked Trump’s credibility is at this point: I’ve got a cellphone full of texts from people who aren’t sure whether to believe Trump actually has Covid,” MSNBC host Joy Ann Reid tweeted. “’He lies so much,’ one friend just texted. ‘Is he just doing this to get out of the debates?’ others are texting.”

Jon Ehrens, a producer for WHYY radio in Philadelphia, estimated on Friday morning that “90 per cent of listener emails/comments are very insistent that the diagnosis is a lie,” tweeting that listeners’ conspiracy theories also included “finding an excuse for why he will lose the election” or “to prove that the coronavirus is no big deal.”

On ABC’s The View, host Sunny Hostin questioned guest Jonathan Karl, a long-time political reporter, about why Trump’s prognosis should be believed, given Trump’s past obfuscations about his health.

“Does this mean that he will downplay his own symptoms? How can we trust any of the information that is coming out of the White House?” Hostin asked. “I personally would prefer to hear information from doctors, not necessarily his physician … but maybe physicians at Walter Reed, or Dr [Anthony] Fauci [the director of the National Institute of Allergy and Infectious Diseases].”

“The sad truth is that we really can’t trust at face value what comes out of the White House on this,” Karl responded, saying that reporters “have to ask the questions” and will try to verify the information they get. “But there’s been so much misinformation that has gone out about the virus, about the pandemic, about things like voter suppression _ it’s really hard to know what to believe.”