What Happened to All the Human Bird Flu Cases?

From the outset of the Trump administration, bird flu, or H5N1 avian influenza, has flown rather conspicuously — and quite mysteriously — under the radar. So much so that this week, the Centers for Disease Control and Prevention announced the end of its emergency response to bird flu, citing the lack of reported human cases. Updates, previously issued weekly, will now arrive monthly. But something isn’t adding up.

At the end of 2024, infections in the United States were surging. From Ohio to California, and in a swath of intervening states, diagnoses were being made in growing numbers of farmworkers who came into contact with infected cattle and poultry. Most suffered a mild spectrum of symptoms — low-grade fevers, muscle aches, inflammation in their eyes. As cases swelled, an older man in Louisiana fell critically ill. He would eventually become the first person in the U.S. to succumb to the virus since initial human cases were reported to the World Health Organization in 1997. We seemed then, for a moment, to be at a tipping point: bound to unleash something both larger and deadlier than we could foreseeably contain, and destined to dust off the cobwebs of a life grimly lived, again, under a pandemic.

And yet, none of that came to pass. Instead, since February, the CDC, which still monitors infections in humans, has not recorded a single new case in the U.S. The count remains the same — stuck firmly at 70.

Rationalizing the lull in infections has been puzzling. Researchers have tied wild birds, the virus’s largest reservoir, and their spring and fall migrations to periods of greater spread of contagion. Cuts to staff who monitored the virus, at the U.S. Department of Agriculture and the Center for Veterinary Medicine, might also be playing a role. But these ideas dismiss the deeper and more fundamental problem around our present grasp of bird flu. As an infectious diseases physician who works primarily with immigrant populations, my perspective often sits at the nexus between the people a novel disease affects and the apparatuses that exist to control it. Lately, the actions of each arm of that equation, no longer motivated by the ethos of a collective concern, are fractured by individual ambitions and epitomize our faltering response.

Cases, in all likelihood, are being missed, in part because detecting infections is simply challenging. Foremost, it requires the ability to recognize an infected person. But this, as we’ve seen, is not always achieved. A number of bovine veterinarians, for example, were found earlier this year to harbor antibodies to the virus — a signature of infection — though none had influenza-like symptoms to suggest they had been infected.

Surveillance, therefore, is largely — and imperfectly — built around those who are exposed and symptomatic. It’s a system that also exposes the vulnerable contexts in which a person may have gotten infected.

In vulnerable groups, this makes a willingness to be tested all the more fraught. According to the Center for Migration Studies, 45% of the agricultural workforce in the U.S. comprised undocumented persons in 2022. And according to USDA data from 2020 to 2022, an additional 19% don’t hold U.S. citizenship. Nearly 80% of American milk is supplied from dairies that employ immigrant labor. Consider a foreign-born dairy hand perplexed by redness in his eyes and a sore throat. He faces a dilemma: After ICE raids like “Operation Return to Sender” targeted farmworkers in California this winter, is getting to the root of his symptoms worth falling into an anti-immigrant governmental maw?

“I can’t argue with anyone who would be risking getting shipped to a Salvadoran gulag for reporting an exposure or seeking testing,” Angela Rasmussen, a virologist at the University of Saskatchewan, told the Associated Press in May. For anyone in this situation, the personal calculus simply does not add up. And so, outreach programs and protective measures have not been sought; infections, if they happen, fester undetected. Lacking granular data from those that might be affected, we are without the empirical information we would typically use to form broader understandings, draw conclusions and map out predictions.

Bird flu is far from a passing peril. It has been detected in almost 1,100 cattle herds across the U.S. In Brazil, the world’s largest exporter of chickens, the first outbreak on a commercial poultry farm was confirmed in May while the country was also investigating about a dozen others. And in Mexico, a 3-year-old girl died from respiratory complications related to the virus. She was the country’s first confirmed human case and was infected by the same D1.1 variant that precipitated severe illnesses in the man in Louisiana and a teenager in British Columbia.

Because infections are still largely constrained to animals and the marginalized people who work with them, bird flu has the distinction of being both omnipresent and barely visible. The way in which one country approaches it will, invariably, have rippling effects in others.

As the focus shifts to the economics of maintaining stocks of chickens and rebalancing the price of eggs, incentives for the testing of farmworkers remain inadequate, and protections among those who are foreign-born are, at best, dubious. From bench to barn, earnest collaborations with scientists and experts are also being undermined. Public health is a delicate concept. To uphold it involves a complex interplay between forces large and, more importantly, small. We can predict the risk of a bird flu pandemic from a single mutation in the virus’s genetic code. An individual, we must also realize, can upend things all the same.