Field Notes #15: Passengers
- Heather McSharry, PhD
- 1 day ago
- 6 min read
In the Margins
One of the things that struck me while researching this week's episode wasn't how difficult it was to discover infection prevention. It was how difficult it was to accept it.
For generations, physicians understood themselves as healers. Their knowledge, skill, and judgment were what stood between life and death. To suggest that they might also be carrying disease from one patient to another challenged medical theory, sure, but it also challenged their identity. That's a surprisingly difficult thing for any profession.
Sometimes progress requires letting go of habits that once signaled expertise. Abandoning explanations that once made sense. Accepting that yesterday's best practice has become today's unnecessary risk.
Medicine has repeated that cycle over and over again. Blood-stained surgical coats gave way to sterile gowns. Bare hands to gloves. Reusable instruments to sterilized ones. More recently, debates over vaccination, masking, and other infection prevention measures remind us that evidence alone won't change behavior and that professional culture changes very slowly.
Maybe that's because infection prevention belongs to a broader family of ideas. Pilots use checklists to ensure that every critical step happens every time, regardless of experience. Scientists use experimental controls to have a definitive way to know the experiment itself worked right. Neither exists because expertise is lacking. They exist because expertise is strongest when it is supported by systems designed to consistently produce reliable outcomes.
Infection prevention asks medicine to do the same. It reminds even the most skilled clinician that good intentions aren't enough and that sometimes the greatest risks to a patient are the unseen things doctors carry with them.
Underlined
Some of the identity shifts medicine has had to make:
From Healer to Potential Vector
For much of history, physicians understood themselves primarily as people who treated disease. Infection prevention expanded that role. Healthcare workers also had to recognize that, without careful precautions, they could become part of the chain of transmission.
From Blood-Stained Coats to Sterile Gowns
Symbols change with science. Blood-stained coats once conveyed experience. Today they would signal contamination. The white coat, sterile gloves, and surgical mask are reminders that medicine's understanding of professionalism has evolved.
From Individual Judgment to Standard Practice
Many of the practices that protect patients today are surprisingly ordinary. Hand hygiene. Sterile technique. Vaccination. Isolation precautions. Checklists. They acknowledge that expertise alone isn't enough.
From Authority to Accountability
Expertise can make change easier but it can also make it harder. The more deeply a practice becomes woven into professional identity, the more difficult it is to question, even when evidence begins pointing elsewhere. Expertise needs introspection.
What It Points To
Progress is possible when expertise is willing to examine itself.
Outbreak Watch
Updates include active outbreaks and emerging signals I'm keeping an eye on. Information is verified through official public health agencies and credible reporting.
As of mid-morning, July 22, 2026:
Active Outbreaks
EBOLA (Bundibugyo, DRC and Uganda) The Bundibugyo Ebola outbreak in the Democratic Republic of the Congo is still expanding. According to the DRC's SitRep#67 there have been 2,473 confirmed cases and 999 deaths, with transmission remaining active across 47 health zones in five provinces. While expanded surveillance is identifying more cases, conflict, displacement, healthcare worker shortages, and limited access to affected communities continue to complicate response efforts. WHO continues to emphasize that the outbreak is unfolding in one of the most operationally challenging environments imaginable.
Uganda, however, has reached an encouraging milestone. The country's most recent patient was discharged on July 16 after two consecutive negative tests, allowing health authorities to begin the 42-day enhanced surveillance period required before the outbreak can officially be declared over. The risk of importation from the DRC remains, but no sustained community transmission has been identified within Uganda.
New World screwworm remains one of the most closely watched agricultural outbreaks in North America. Since last week's update, confirmed cases have increased from 37 to 41, the number of affected premises is now 32, and the outbreak has expanded from 13 to 15 Texas counties, while remaining present in one New Mexico county. Response efforts continue to focus on rapid detection, animal movement restrictions, treatment of infested livestock, and large-scale releases of sterile male flies to prevent the parasite from becoming permanently reestablished.
This week also brought an encouraging operational milestone. USDA has now officially designated the Metapa sterile fly production facility in Mexico as operational. The facility, completed in late June, is ramping toward a production capacity of 100 million sterile flies per week, confirming that regional sterile fly production is beginning to expand.
Even so, the overall capacity gap remains substantial. Combined production from the long-established Pacora facility and Metapa is expected to reach roughly 200 million sterile flies per week once Metapa reaches full capacity. Experts estimate that 500–600 million sterile flies per week may ultimately be needed to support a robust regional eradication campaign. Construction of the Moore Air Base production facility, expected to add another 300 million flies per week, continues.
For me, this slightly changes the forecast. The outbreak continues to expand geographically, but the response infrastructure is finally beginning to catch up. The next signal I'll be watching is whether the facility consistently reaches its projected production capacity. That production rate will tell us far more about the campaign's long-term prospects than the operational designation alone.
Cyclosporiasis (United States)
The country's largest recorded Cyclospora outbreak continues while investigators work to identify the contaminated food source. Michigan remains the epicenter, now reporting 7,171 confirmed cases, almost twice the number reported a week ago. The CDC’s national dashboard remains seriously behind state reporting.
Over the past week, the investigation took an unexpected turn.
FDA initially announced that a sample of shredded iceberg lettuce supplied by Taylor Farms de Mexico had tested positive for Cyclospora. Days later, agency scientists re-reviewed the laboratory data and determined the result was a false positive, highlighting just how technically challenging it is to detect this parasite in food.
Importantly, that does not mean Taylor Farms has been ruled out. The epidemiologic investigation and traceback analysis continue to converge on shredded iceberg lettuce from Taylor Farms de Mexico. At this point, there are no laboratory-confirmed positive product samples, but there is still strong epidemiologic evidence linking one defined cluster of illnesses to shredded iceberg lettuce supplied by Taylor Farms de Mexico and served at certain Taco Bell locations in five states. But the distribution footprint is broader than that cluster.
There is a voluntary recall in effect to remove all iceberg lettuce sourced from central Mexico from the U.S. market, including specified Marketside products sold at Walmart, while FDA continues investigating what other restaurants and retailers may have received the implicated supply. The Taco Bell cluster is where the evidence is strongest—not necessarily the only place exposure occurred.
Biological Signals
Case numbers in Central Africa have begun to stabilize, but I'm increasingly interested in what happens beyond the outbreak itself. Clade I mpox has now appeared in multiple countries outside its historic range, and I'm watching to see whether these remain isolated importations or begin establishing sustained transmission in new settings. I'm watching its geographic spread but also whether it's successful establishing sustained transmission outside its historic range.
Oropouche is another virus I'll be following more closely. Once largely confined to the Amazon Basin, Oropouche virus has expanded into new regions of South America and the Caribbean over the past two years, with travel-associated cases subsequently reported in North America and Europe. I'm watching whether that geographic expansion continues and whether changing vector ecology creates opportunities for the virus to establish itself in new regions.
I'm continuing to watch H5 for evidence that the virus is changing how it behaves in mammals. Individual spillover events aren't the signal. The signal is whether they begin occurring more frequently, involve new species, show sustained mammal-to-mammal transmission, or reveal evidence of adaptation to mammalian hosts.
No major new biological signals emerged this week. That absence is encouraging. But because influenza evolves incrementally rather than all at once, H5 will remain on this watchlist.
Postscript
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If July's Turning Points series has taught us anything, I hope it's this: "An ounce of prevention is worth a pound of cure" has survived for generations because, when prevention is possible, it's true.
Lately, though, we've been hearing a different message—that prevention is optional, that natural infection is preferable, or that we can simply treat diseases after they appear. That's a comforting idea. Unfortunately, biology doesn't care whether an infection is "treatable."
Measles is a good example. Survival isn't the same as harmlessness. Measles temporarily erases part of the immune system's memory, leaving children more vulnerable to other infections for months to years afterward. Vaccination doesn't just prevent measles, it helps preserve the immune protection children have already built against countless other pathogens. Preventing disease avoids the damage that treatment can never fully undo.
And speaking of treatments that fall short, next week we'll leave the hospital behind and, with Kate at our side, step through an unmarked door into a 1920s speakeasy for an OAD experience you won't want to miss.
Until then, stay curious.
— Heather
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