"They develop drugs like the antibiotics … you see … antibiotics used to solve every problem. Now one of the biggest problems the world is the germ has gotten so brilliant that the antibiotic cannot keep up with it.
"And they're constantly trying to come up with a new … people go to the hospital and they catch … they go for a heart operation — that's no problem — but they end up dying from … from … problems.
"You know the problems I'm talking about."
Trump added: "There's a whole genius to it. It's hidden but it's very smart."
A video clip of the bizarre ramble has attracted more than three million views on Twitter in less than 24 hours and plenty of ridicule.
"Fact check: Antibiotics have *never* worked against viruses," tweeted Australian media expert Dr Belinda Barnet.
Ms Krassenstein wrote: "My 6-year-old nephew knows that antibiotics are useless on ALL viruses. Donald Trump does not! How can such a stupid man be our President?"
British lawyer and activist Dr Shola Mos-Shogbamimu tweeted: "Vaccines not Antibiotics fight viruses.
"It's called #coronavirus for a reason. The audacity of Trump propping his ignorance of medicine as authority will get Americans killed #TrumpVirus. #TrumpPressConference does more damage than good. The US & UK are screwed."
Australian virologist Ian Mackay said simply: "Oh ffs!"
• Covid19.govt.nz: The Government's official Covid-19 advisory website