In the search for the swine flu outbreak’s “ground zero,” blogs have called upon mainstream media to investigate the potential role of large factory farms in breeding and spreading the virus.

Major news outlets have tentatively begun to do just that over the last two days. Reports have focused on the town of La Gloria, Mexico, where the first known victim was identified. (He has since recovered.) La Gloria is located close to a million-pig farm, Granjas Carroll, which is partly owned by Smithfield Foods, an American company that is the world’s largest producer and processor of pork products.

So far, however, there is no evidence of a direct connection between the farm and the swine flu virus. But there are reasons to both suspect and doubt that such a connection exists, and this has led to sporadic arguments among reporters covering the outbreak about the line between asking tough questions and jumping to conclusions.

The first blogger to implicate industrial hog farms was Grist’s food editor, Tom Philpott, in a Saturday post headlined, “Swine-flu outbreak could be linked to Smithfield factory farms.” Philpott cited a swine-flu timeline posted by the blog Biosurveillance, as well as articles in the Mexican newspapers La Marcha and La Jornada, which had reported that residents of La Gloria suspected the Granjas Carroll farm of spreading sickness via “clouds of flies” that travelled between the two. Philpott’s assessment was that:

[T]he possible link to Smithfield has not been reported in the U.S. press. Searches of Google News and the websites of the New York Times, Washington Post, and Wall Street Journal all came up empty. … I’ll be in touch with contacts in Mexico as this story develops —and I’ll be curious to see whether the U.S. media explores the link with Smithfield’s Mexico operation.

At The Huffington Post on Sunday, freelance reporter David Kirby commented on the recent spread of industrial-scale hog farms, or confined animal feeding operations (CAFOs), in Mexico, suggesting that:

U.S. and Mexican epidemiologists and veterinarians will surely want to take swine samples from Mexican CAFOs and examine them for the newly discovered influenza strain (No one knows exactly how long it has been in circulation). And though it is too early to know if this new virus mutated and incubated on Mexican hog CAFOs, the industrialized facilities unquestionably belong on the list of suspects.

“This should be one of the big second-day stories of this remarkable news event,” argued Tom Yulsman at the Center for Environmental Journalism on Tuesday, in a blog post headlined, “What mainstream media aren’t telling you about the swine flu outbreak.” Yulsman pointed to a recent report from the Pew Charitable Trusts and Johns Hopkins Bloomberg School of Public Health, which found that “Animals in such close confinement, along with some of the feed and animal management methods employed in the system, increase pathogen risks and magnify opportunities for transmission from animals to humans.”

Mainstream media granted Philpott and Yulsman’s wish for more coverage almost as soon as they’d made it. Major outlets have been far more skeptical and restrained in their reporting about the CAFO hypothesis, however. The reason is that, so far, authorities have yet to find an infected pig in Mexico, let alone at the Granjas Carroll farm. None of the pig farm’s workers appears to be sick, either.

The result is that most mainstream news articles—such as those in The New York Times, The Washington Post, and The Wall Street Journal—have included only a paragraph or two about Granjas Carroll in larger stories about La Gloria being a prime candidate for the flu outbreak’s origin. The Associated Press and CNN’s Sanjay Gupta visited Granjas Carroll, but only the former got in.

Curtis Brainard is the editor of The Observatory, CJR's online critique of science and environment reporting. Follow him on Twitter @cbrainard.