Infant Formula Botulism, Swine Flu, & Animal Outbreaks

In this episode of Thermometer HQ, I sat down with my friend and colleague Dr. Jon Epstein to trace a single thread through a series of very different outbreaks: how what’s happening in barns, fairgrounds, rodeo arenas, and pig farms can change what ends up on our plates—and how safe we are when it gets there.

We recorded this just after Thanksgiving, a time when many of us sit around a table and say we’re grateful for our health. On Inside Outbreaks, Jon and I spend a lot of time talking about the ways that health is threatened. But this week’s episode is really about how systems—public health, veterinary health, and food safety—either protect that health or quietly fail in the background.

Infant formula botulism: a missed signal in our most vulnerable

We start with the ongoing infant botulism outbreak linked to ByHeart Whole Nutrition Infant Formula. At least 37 confirmed or suspected cases have been reported across 17 states. That’s not just a statistic—that’s dozens of families who did what they were supposed to do, fed their child a regulated product, and still ended up in an ICU watching their baby struggle to move or breathe.

Botulism in infants is caused by Clostridium botulinum, a bacterium that produces one of the most potent toxins known. In babies, it can cause profound, life-threatening paralysis. The only way to prevent deaths is early recognition and rapid treatment.

What’s especially troubling about this outbreak is the timeline. California public health officials have now confirmed six additional formula-linked infant botulism cases that occurred between November 2024 and June 2025—months before the broader outbreak was recognized. That means this cluster was smoldering for at least nine months before our systems connected the dots.

This is exactly why we invest in surveillance. We rely on a chain: clinicians order the right tests, labs report results, and public health agencies analyze patterns across people, places, and time. When any link is weak—understaffed health departments, fragmented data systems, overworked clinicians—signals get missed. In this case, the “signal” was babies becoming paralyzed by contaminated formula. There is no stronger argument for strengthening public health capacity than that.

And as Jon pointed out, manufactured foods raise the stakes. Unlike a bad potato salad at a picnic, contaminated formula or processed foods move through interstate commerce. When something goes wrong, it’s not a local problem—it’s a multi-state event.

H1N2 swine-origin flu in Vermont: why one case matters

We then turned to influenza, specifically a human infection with a swine-origin H1N2 variant virus detected in Vermont. This isn’t seasonal flu and it isn’t the highly publicized H5N1 bird flu. It’s a reminder of something we talk about a lot but people understandably tune out: there are many different flu viruses, and pigs are important mixing vessels for them.

The patient in Vermont was hospitalized briefly and recovered. On an individual level, that’s good news. From a public health standpoint, the story is how the virus was detected. A specimen from this patient was forwarded to CDC, where specialized testing showed it was a novel variant flu linked to pigs.

That’s flu surveillance doing exactly what it’s supposed to do: scanning for unusual variants so we can respond before they spread. It’s also a reminder that even during times of political dysfunction and budget cuts, we desperately need these backbone systems to keep running.

E. coli at the state fair: microbes in the petting zoo

Our next stop was the Arizona State Fair, where at least eight children were hospitalized with Shiga toxin–producing E. coli infections after visiting the petting zoo—most of them having petted pigs. For families, these are supposed to be wholesome memories. Instead, they turned into ICU admissions and, in some cases, the risk of kidney failure.

This hit close to home for me. Early in my CDC career, I investigated similar outbreaks at county fairs in Ohio. In one case, we found E. coli O157 contamination throughout a show barn—on the floors, in the sawdust, even up on the rafters. Animals had shed the bacteria in their feces earlier in the week; by the time of a closing-night dance, people were literally inhaling contaminated dust kicked up from the floor.

Jon shared his own CDC story: a rabid bear at a fair’s petting area that led to a massive effort to track down everyone who had touched it. Fortunately, there were no human rabies cases, but the episode underlined how thin the line can be between a charming animal encounter and a public health emergency.

We’re both clear on this: fairs and petting zoos are valuable. They connect people to agriculture and animals. But basic biosecurity—especially handwashing stations, clear signage, and keeping visibly ill animals out of public contact—is non-negotiable. And for parents, the boring advice is still the lifesaving advice: wash kids’ hands before they eat, keep pacifiers and sippy cups off barn floors, and assume that anything near animal pens could be contaminated.

Equine herpesvirus: devastating for animals and livelihoods

From there we moved to an outbreak that doesn’t affect humans at all: a multi-state outbreak of equine herpesvirus (EHV) traced to the Women’s Professional Rodeo Association World Finals in Waco, Texas. At least 16 horses across multiple states have developed neurologic disease.

EHV is to horses what some herpesviruses are to humans: widely carried, often dormant, but capable of reactivating under stress. In most horses, infection is mild and respiratory. But when the virus affects the nervous system, the result can be staggering, paralysis, and death.

This is not a zoonotic disease—but it deeply affects people’s livelihoods and emotional health. Horses are athletes, companions, and therapy partners. Losing a string of competition horses can be economically catastrophic.

What’s striking here is that we have tools that work: EHV vaccines and simple infection control practices. The vaccines don’t prevent all infections, but they reduce severe disease and viral shedding. As I half-joked on the show, it will be interesting to see whether anyone who is skeptical about vaccines for humans suddenly embraces them for their horses when their livelihood is at stake.

African swine fever: when animal outbreaks threaten the food system

We closed with African swine fever (ASF) in Spain and the UK’s decision to ban pork imports from affected areas. ASF is a viral disease of pigs and wild boar. It does not infect humans, but it is highly contagious and often fatal in pigs. Once ASF gets into a herd, the standard response is brutal but necessary: depopulate the farm, disinfect, and start over.

For Spain—the EU’s top pork producer—this is not just a veterinary problem. It’s a national economic crisis with ripple effects across Europe’s food supply. For countries like the United States, it’s a warning shot. We remain free of ASF on the mainland, but the virus circulates in parts of Africa, Asia, Europe, and occasionally the Caribbean. Given how resilient the virus is in meat products and on equipment, keeping it out requires constant vigilance.

When you zoom out, a pattern emerges. Three of the major animal protein sources in the American diet—poultry, cattle, and pigs—are all facing serious infectious threats: H5N1 in poultry, parasitic infections and other emerging diseases in cattle, and ASF in pigs. Protecting human health now means protecting the animals we depend on and the systems that raise, move, and process them.

Jon and I ended by talking about choices. Not everyone can, or wants to, give up animal protein. But many of us can choose to support local producers, diversify our protein sources, and push for stronger biosecurity and surveillance throughout the food chain. Those aren’t abstract policy ideas; they’re practical steps that make it less likely your holiday meal is disrupted by the next major animal outbreak.

If there’s one takeaway from this episode, it’s this: the line between “animal outbreak” and “human problem” is vanishingly thin. Investing in public health, veterinary health, and safer food systems isn’t just about avoiding disaster—it’s about preserving the everyday health we say we’re grateful for around the table.

👉 Watch the full episode on YouTube: https://youtu.be/5cRwzc9rb6M