WASHINGTON, Oct. 6 (Reuters) - Democratic presidential candidate Joe Biden said on Tuesday (Oct 6) that next week's scheduled debate with Republican US President Donald Trump should not take place if Trump is still infected with COVID-19.

Biden said the Oct 15 debate in Miami should only be staged under strict health guidelines and called the coronavirus outbreak that has seen Trump and other White House officials infected "a very serious problem".

"If he still has COVID-19, we shouldn’t have a debate," Biden told reporters after a campaign stop in Pennsylvania.

"I’m not sure what President Trump is all about now. I don’t know what his status is. I’m looking forward to being able to debate him, but I just hope all the protocols are followed," Biden said.

Asked about Biden's comments, Trump campaign spokesman Tim Murtaugh said: “President Trump will be healthy and will be there. There’s no getting out of this one for Biden, and his protectors in the media can’t cover for him.”

After days of conflicting messages from doctors and aides about his condition, Trump, 74, returned to the White House on Monday after three nights at a hospital. His doctor said on Tuesday that Trump reported no COVID-19 symptoms and was doing "extremely well".

The normal quarantine period for anyone testing positive for the novel coronavirus is 14 days. Trump announced his positive test on Friday.

But the disease continues to spread among Trump's top aides, with White House senior policy adviser Stephen Miller saying he tested positive on Tuesday.

"Too many people have been infected. It’s a very serious problem, so I will be guided by the guidelines of the Cleveland Clinic and what the docs say is the right thing to do," Biden said of his debate participation.

The former vice president, 77, tested negative again for COVID-19 on Tuesday, a week after sharing a debate stage with Trump in Cleveland.

Vice President Mike Pence and Biden's running mate, US Senator Kamala Harris, will hold their scheduled debate on Wednesday night in Salt Lake City.

The US Centers for Disease Control and Prevention said it was safe for Pence to take part in the debate because he was not in close contact with anyone with COVID-19, including Trump.