Infant Formula Botulism, Ethiopia Marburg, and New H5N5 Bird Flu

In this episode of Thermometer HQ’s Inside Outbreaks, I sit down with my colleague Dr. Jon Epstein to unpack three very different but closely connected stories: a multi–state outbreak of infant botulism linked to contaminated formula, Ethiopia’s first-ever cases of Marburg virus disease, and the first documented human infection with H5N5 bird flu in the United States. Together, they highlight a single theme: when our surveillance systems are weak, outbreaks don’t go away—they simply become harder to see until they are much harder to control.

Why surveillance still matters more than ever

After weeks of uncertainty during the U.S. federal government shutdown, it has been a relief to see disease surveillance systems flicker back to life—data returning to websites, lab reports flowing again, people back at the jobs they were trained to do. For people like Jon and me, “no news” about outbreaks isn’t comforting; it’s terrifying. If you don’t have eyes on the problem, you only find out when it’s already an emergency.

The three stories we discuss this week are exactly the kind of events you only detect if public health agencies are staffed, resourced, and allowed to do their work.

Infant botulism and the ByHeart formula recall

The first and most emotionally charged story involves infants: a population that is uniquely vulnerable to infectious diseases. As of November 14, 2025, health officials have identified 23 cases of infant botulism across 13 U.S. states, all linked to ByHeart Whole Nutrition infant formula. The bacteria that causes botulism, Clostridium botulinum, was found in an open container of the formula, triggering a nationwide recall.

Botulism is rare, but it is one of the most feared bacterial diseases because of how it works. C. botulinum produces a powerful neurotoxin that blocks the signals nerves use to tell muscles to move. When that toxin affects the muscles involved in breathing, paralysis can be fatal without intensive care and rapid treatment.

There are two key forms of botulism people should know about:

• Classic foodborne botulism: You ingest pre-formed toxin in contaminated food, often from improperly canned or preserved products. CDC maintains a special stockpile of antitoxin to treat these cases.
• Infant botulism: Instead of ingesting the toxin, infants ingest spores. Because babies’ guts and microbiomes are still immature, those spores can germinate in the intestine and begin producing toxin inside the body.

That second scenario is what we’re dealing with here. The treatment is also different. Infants with botulism receive botulism immune globulin, a specialized product produced by the California Department of Health and supplied for the entire country. It’s one of those quiet examples of how strong state health departments effectively function as “mini-CDC’s,” stepping in with expertise and resources that benefit the nation as a whole.

A common follow-up question I get is: If this is so rare, why have I heard that babies shouldn’t eat honey? The reason is exactly the same—C. botulinum spores are found widely in the environment, including in honey. That’s why we advise no honey for children under one year of age.

Even though infant botulism is rare—roughly 100 cases per year nationwide—the severity of illness means that a contaminated formula product is an unacceptable risk. This outbreak is a reminder that even well-regulated, highly controlled manufacturing environments can fail, and that we rely on FDA and public health agencies to detect, investigate, and correct those failures quickly.

Marburg virus appears in a new place: Ethiopia

The second story brings us to East Africa. On November 14, Ethiopia confirmed its first-ever outbreak of Marburg virus disease—nine cases in the Omo region in the south of the country, near the border with South Sudan. Genetic analysis shows the virus is a strain previously detected in other East African countries, but Ethiopia itself has not previously reported viral hemorrhagic fever outbreaks.

Marburg virus belongs to the filovirus family, the same group as Ebola. These viruses cause severe hemorrhagic fevers, with average fatality rates around 50% and the potential to be much higher in settings without adequate medical care. Early symptoms—fever, body aches, gastrointestinal complaints—are nonspecific. But as the disease progresses, patients may develop bleeding, organ failure, and shock.

We know far more about the ecology of Marburg than we do for some other hemorrhagic fevers. The natural reservoir is the Egyptian rousette bat, a fruit bat species found across large parts of Africa and the Middle East. These bats live in enormous colonies—hundreds of thousands of animals—in caves and mines. People are typically infected through activities that bring them into those environments: caving, mining, or sometimes ecotourism.

In Ethiopia’s Omo region, there are extensive cave systems, including the Sof Omar caves, one of the largest in Africa and an emerging tourist destination. We don’t yet know whether the current patients visited those caves, worked in local mines, or had other exposures, but that is exactly the kind of detective work outbreak teams from Ethiopia’s Ministry of Health, Africa CDC (headquartered in Addis Ababa), and WHO will now undertake.

Two key points for context:

• Marburg is terrifying but not easily pandemic-prone. Like Ebola, it spreads mostly through close contact with very sick people—their blood and body fluids, contaminated surfaces, or unsafe burial practices. That makes it devastating locally, especially for families and health workers, but less likely to explode into a global pandemic.
• Outcomes depend heavily on supportive care. With intensive care—fluids, blood products, respiratory support, and careful management of complications—many patients can survive. Unfortunately, Ethiopia’s ICU capacity is limited. There are skilled clinicians, but far too few fully equipped intensive care units.

This outbreak is a sobering reminder that as land use, mining, and ecotourism expand into previously less-disturbed areas, spillover events from wildlife to humans will continue. Our job is to detect them quickly, protect people at highest risk, and strengthen local health systems so that severe cases are survivable, not automatically fatal.

A new bird flu threat: the first human H5N5 case in the U.S.

The third story brings us back to the United States and to a virus that has been on our radar all year: avian influenza. On November 13, Washington State reported a human infection with H5N5 highly pathogenic avian influenza in Grays Harbor County—the first human case of H5N5 ever reported worldwide, and the first human bird flu case in the U.S. in nine months.

This is not the H5N1 strain we’ve discussed extensively on Thermometer HQ. H5N5 is another subtype that has primarily circulated in birds, but it has previously infected mammals such as foxes, raccoons, and skunks in Canada, often causing severe or fatal disease. Experimental models suggest it is not yet well adapted to spread efficiently between mammals, which is good news—but the line between “not yet” and “now” can be thin with influenza.

In this case, the patient is an older adult who presented with high fever, confusion, and respiratory distress—an unequivocally severe illness. Investigators report that the individual keeps a mixed backyard flock of domestic poultry, and that those birds had exposure to wild birds. That combination—human, domestic animals, and wildlife sharing the same air and environment—is where influenza finds “room to maneuver,” swapping genes and exploring new evolutionary pathways.

Two things worry me most here:

1. Spillover is becoming routine. We now see repeated introductions of avian influenza into poultry, dairy cattle, and wildlife in North America. Each spillover event is another roll of the dice. Even if H5N1 never becomes efficiently transmissible between humans, another reassorted virus—perhaps involving segments from H5N5—could.
2. We are probably missing mild cases. Our influenza surveillance system is built to flag unusual strains, and in this case it did its job. But the people most exposed to infected poultry and cattle in the U.S. are often migrant workers, many of whom are undocumented. Aggressive immigration enforcement, fear of job loss, and under-resourced public health agencies all discourage testing and reporting.

Severe cases end up in hospitals and get attention. The early, mild, or unusual cases—the very ones that would signal a virus beginning to adapt to human-to-human transmission—are easy to miss in communities that fear contact with government institutions.

The common thread: strong public health is invisible until it’s gone

Taken together, these three outbreaks tell a consistent story:

• We detected the infant botulism outbreak because states and CDC were actively investigating, testing, and sharing data.
• Ethiopia found and confirmed Marburg because it had enough laboratory capacity and regional support to recognize a hemorrhagic fever it had never seen before.
• Washington State picked up H5N5 because clinicians and laboratories were part of a functioning influenza surveillance system.

When we defund or politicize public health agencies, or drive vulnerable workers away from care and testing, we don’t eliminate risk—we blindfold ourselves. If we want to be ready for whatever comes next, we need to invest in surveillance, laboratories, and the people who staff them, from county health departments all the way to international institutions.

If you’re a clinician, policymaker, or simply someone who wants to understand the infectious disease risks that shape your world, my hope is that Thermometer HQ helps you make sense of these events without sensationalism—just facts, context, and practical implications.

👉 Watch the full episode on YouTube: https://youtu.be/I7me3B8RdRw