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There's been only one human case of bird flu in this outbreak. Are we missing others?

AILSA CHANG, HOST:

Now some reassuring news on bird flu. Federal officials say extensive testing of dairy products shows no infectious virus. But there are still big unknowns, like whether the U.S. is catching any possible human cases. NPR's Will Stone reports.

WILL STONE, BYLINE: Officially, there is only one documented case of bird flu spilling over from cows into humans during this outbreak. But Dr. Gregory Gray suspects the true number is higher based on what he's heard from some veterinarians, farm owners and dairy workers in Texas.

GREGORY GRAY: We know that some of the workers sought medical care for influenza-like illness and conjunctivitis at the same time the H5N1 was ravaging the dairy farms.

STONE: Gray is an epidemiologist at the University of Texas Medical Branch in Galveston.

GRAY: I don't have a way to measure that, but it's biologically quite plausible that they, too, are suffering from the virus.

STONE: Gray has spent decades studying respiratory infections in people working with animals. He says the virus is probably more widespread in cattle than the nine states identified.

GRAY: And possibly spilling over much more to humans than we knew or than we know.

STONE: Genetic sequencing doesn't indicate the virus has evolved to easily spread among humans. It's still not clear exactly how a person would catch this from a cow. But epidemiologists like Jessica Leibler at Boston University say it's still critical to look for any additional cases. Some could be flying under the radar if they're mild, like the one documented in a Texas dairy worker.

JESSICA LEIBLER: That is distinct from saying there have been human cases of H5N1 where people are really sick.

STONE: It's not surprising that some cases could have gone undetected earlier in the outbreak. On Wednesday federal officials said around 25 people have been tested so far. That feels low to Leibler, who has studied the risk of flu spreading from animals to workers.

LEIBLER: If the idea was to try to identify where there was spillover from these facilities to human populations, you'd want to try to test as many workers as possible.

STONE: The health care system would likely catch any alarming rise in human cases of bird flu, especially if the illnesses are severe. The Centers for Disease Control and Prevention monitors emergency departments and hospitals and hundreds of clinical laboratories. Plus, the agency told clinicians to be on the lookout. But even these safeguards may not be sufficient if cases spread quietly. Here's Dr. Mary-Margaret Fill, deputy state epidemiologist for the Tennessee Department of Health.

MARY-MARGARET FILL: I worry a bit that if we wait until we see a spike in those systems that perhaps we would already be seeing much more widespread community transmission.

STONE: Of course, all of this requires buy-in from dairy farmers, too. Veterinarian Fred Gingrich directs the American Association of Bovine Practitioners. He says dairy farmers are deeply concerned about keeping their animals and workers safe. But he points out they do not get compensated if they alert the government to suspected cases in their herd.

FRED GINGRICH: So what is their incentive to report?

STONE: That's in contrast to poultry farmers who do get paid for their losses.

GINGRICH: It's the same virus. It just doesn't kill our cows.

STONE: There are also real challenges in reaching those who work with these animals. Dr. Gray knows this from his own research.

GRAY: They live remotely from health care. They may not have insurance. There may be some questions on immigration status.

STONE: Gray has started looking for evidence of human spread on several dairy farms that dealt with the virus. To do that, he's promised anonymity.

GRAY: So we wouldn't identify the farms where we are collecting specimens.

STONE: It was actually part of a study that he initially launched to look at possible spillover of the virus that causes COVID, but now there's another virus he's chasing. Will Stone, NPR News. Transcript provided by NPR, Copyright NPR.

Will Stone
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