LONDON — The photo of a sick 4-year-old boy lying on the floor of an overcrowded hospital in Yorkshire because there were no beds available for him sent a jolt through the British election.

A local newspaper, the Yorkshire Evening Post, had published a story about the episode on Sunday after the boy’s mother reached out to share her outrage about the experience. The hospital, Leeds General Infirmary, confirmed that the incident had indeed happened, and issued an official apology.

Then on Monday, three days before Britain’s general election, the story was splashed on the front page of The Daily Mirror, a left-leaning tabloid, to criticize the health care policies of Prime Minister Boris Johnson’s Conservative Party. Later on Monday, Mr. Johnson was shown the photo in an awkward television interview with ITV that went viral online.

It all seemed like a fairly normal cycle of political outrage.

But since Monday evening, journalists and researchers have tracked what appears to be a social media campaign to discredit the boy’s family. A message was shared widely on Facebook and Twitter from somebody claiming to know a nurse at the hospital who said the mother had staged the photo.