On Tuesday morning, Ms. Porritt told The Times that the W.H.O. report should have said that “about half of infections are due to needle injection, some of which is deliberate self-infection.”

It was not clear, though, whether there was evidence to say even that much. The various reports included no apparent documentation of any cases.

By Tuesday afternoon, the W.H.O. had issued its own correction: “The sentence should read: ‘Half of the new H.I.V. cases are self-injecting, and out of them, few are deliberately inflicting the virus.’ ” Later in the day, it retracted that statement, too, and said instead, “There is no evidence suggesting that deliberate self-infection with H.I.V. goes beyond a few anecdotal cases.”

The Greek H.I.V. claim did not receive much attention when the report first came out, though it was mentioned in an article late October on the website of the magazine New Scientist. But the claim gained traction quickly Monday on Twitter, and it was reposted by European journalists and politicians.

A Sky News headline said “Greeks ‘Injecting HIV to Claim €700 Benefits’ ,” while a Fox Business headline said “European Crisis: Half of HIV Infections in Greece Are Self-Inflicted.”

Not all accepted it at face value, however. Media Matters for America, a liberal media watchdog group, wrote online Monday that “the W.H.O. report is incorrect,” after studying the citation.

What is not in dispute is that while Greece saw a sharp rise in cases of H.I.V., the virus that causes AIDS, with the onset of its economic crisis, the latest government figures show the number of new cases falling this year.