Not to mention corruption
Jess Steier, DrPh
A few characteristics of Cyclospora make it
tricky to chase down. Because it will
not grow in culture, the standard playbook doesn't apply. With most
foodborne bacteria, a lab grows the organism, sequences it, and uploads the
genetic fingerprint to PulseNet, the national network
that flags when a case in one state matches a case in another.
The US Centers for Disease Control and Prevention (CDC) has instead been working from partial genotyping, because Cyclospora's genome is complicated enough to defeat the sequencing methods that work for bacteria.
Cyclospora contamination on produce is often sparse
and unevenly distributed, and it tends to sit close to the limit of what a test
can detect, which is how contaminated lettuce ends up testing clean.
Investigators were left with the oldest tools in the kit: interviews and
shipping records.
Important early clues widely missed
If you have young kids you know exactly why. They are
devoted fruit eaters. (I used to joke that my daughter was going to turn into a
strawberry.) But more spotty toward veggies.
That narrows things, but the hunt continues. There are other
important factors, too, like understanding how a growing region is organized
into blocks, when each produce item was cut and by whom, how product from
different fields gets combined at a processor, how long it takes to move from a
field in central Mexico to a restaurant in Michigan, and how fast a perishable
product cycles off the shelf.
That knowledge does more than point at a culprit. It also helps estimate how many people could have been exposed and where. It tells you when contaminated products should have cleared the shelves and new exposures should stop, even though reported counts will keep climbing for weeks afterward. Because molecular typing cannot deliver the clean fingerprint that is available in a bacterial outbreak, it is also central to deciding whether a case in one state belongs with a case in another. Trace-back is a supply chain exercise as much as an epidemiologic one.
Michigan went through ingredient-level
food histories from 190 people who had eaten at Taco Bell before
falling ill, and 90% of them had eaten iceberg lettuce. The FDA's trace-back
investigation followed the paper backward, converging on one supplier and then
on a single independent farm in central Mexico that Taylor Farms says accounts for less
than 1% of the US iceberg supply. The recall came July 17.
9 states in the outbreak, but 41 affected overall
This is the largest documented Cyclospora outbreak
in US history, and the coverage has that part right. What has reached the
public is a scary number that keeps going up.
It misses the fact that, while cyclosporiasis—which is what
a Cyclospora infection is called—has now been reported in 41
states, the
outbreak is only in nine. The numbers being reported measure different
things. The CDC and Food and Drug Administration (FDA) have included 1,947
confirmed cases in the nine-state Taco Bell outbreak, which
epidemiologic and trace-back evidence links to iceberg lettuce, while the CDC
separately reports more
than 4,000 confirmed domestically acquired cases nationally since
May.
In addition, thousands of samples from patients are still awaiting
CDC confirmation, plus several hundred more in travelers who got sick abroad.
Some states count probable and confirmed cases together, so their totals run
higher still. Stack all of it, as plenty of coverage has, and you get a single
national outbreak that doesn't exist.
Consider what happened when the CDC added four states to the
outbreak on July 24. It read as though the outbreak had spread, but
investigators think those patients
may have gotten sick around the same time as the patients in the
original five states, and simply took longer to connect to the same
source.
Stack all of it, as plenty of coverage has, and you get a
single national outbreak that doesn't exist.
Cyclosporiasis turns up somewhere every summer, following a
seasonal pattern that is well established even if its exact causes are not, and
outbreaks are frequently tied to fresh produce. Several states, including
California and New Jersey, have said their counts this year are running in line with
typical seasonal trends. North Carolina thinks its own increase is
about parsley and cilantro, neither of which has emerged as a national
signal, and the FDA is separately investigating a
cluster of at least 72 people with no source identified at all.
Folding all of that into one running total costs us more
than public calm. It hides the possibility that several outbreaks are happening
at once.
Illinois, one of the four states added last week, says its
July case reports are running at levels the
state has not seen since 2018. Illinois is right that 2018 is the year
to think about, though the important lesson isn't the case count. That summer
brought 511 cases tied
to a Fresh Express salad mix served at McDonald's, 250 tied to Del Monte
vegetable trays, and a
third outbreak in Texas that never had a source identified at all.
A cumulative tally is a surveillance instrument, and an
important one, but it does not tell you whether you are at risk this week,
which is the very thing people want to know.
Picture one person inside that count. She eats a salad at
the end of June and feels fine for a week. She spends a few more days assuming
it's a stomach bug, sees a doctor in the second week of July, and gets tested
only because someone thinks to request Cyclospora testing,
which many routine stool tests and gastrointestinal panels don't include. The
lab confirms toward the end of the month. Her interview comes after that.
Whether she belongs to this outbreak or to the ordinary summer background data
may not be settled until August.
Every case on every one of those charts is carrying some
version of that lag, which is why the FDA has said confirmed
counts will keep climbing well after the recall.
Likely more than one wave of exposure
On July 24, the CDC finally published an epidemic curve for
this outbreak, plotting the 1,947 outbreak-associated cases by illness
onset rather than by report date. There are two distinct peaks: one (when the
person first had symptoms) cresting around June 25 and a second (when the
sickness was reported) around July 10, with a deep valley between them.
That separation is substantial enough to suggest exposure
may have come in more than one wave. Working back through Cyclospora's
usual incubation period of about a week would place those exposures near
mid-June and again around the start of July. Lettuce isn't harvested once a
season and held in storage like corn or soy. It's cut more or less continuously
and eaten within days, so illness follows fairly closely behind whenever the
contaminated product moved. That makes a gap this deep more consistent with
separate windows of exposure than with one prolonged stretch of it.
A cumulative tally is a surveillance instrument, and an
important one, but it does not tell you whether you are at risk this week.
The first of those illness peaks had risen and fallen before
the CDC issued its health advisory on July 14, and before the FDA publicly
named the lettuce two days later. Whether the two waves represent separate
contamination episodes—one product contaminated intermittently across different
harvest lots, or something else—the curve alone cannot say, and nobody else has
either. It arrived the same day the outbreak grew to nine states, a week after
the recall and long after the story had largely been told as one steadily
rising national number.
Producing that picture is the one thing no state could have
done on its own. Michigan posts case counts by
date reported, updated weekly and labeled accurately as such. Others
post illness-onset curves, or county maps, or twice-weekly tallies. Every one
of those answers a question about a single jurisdiction, and none of them can
tell you whether two states are experiencing the same outbreak, because no
state can answer a multistate question using its own data no matter how
carefully those data are collected. That assembly sits a level above all of
them, and it took until the fourth week of July.
Too late, and then too fast
The messaging made it worse. The CDC's Health Alert Network advisory arrived
July 14, roughly 10 weeks after the CDC began receiving reports of a national
rise in cases.
Days later, the FDA published notice of a Cyclospora-positive
lettuce sample on Saturday, July 18, retracted
it the next day, and didn't explain the sequence until the afternoon of
July 20. That sample had come from routine border screening rather than from
recalled product, and the epidemiologic and trace-back case implicating Taylor
Farms lettuce never rested on it. By then "false-positive" had run
the news cycle, and plenty of people came away thinking the company had been
cleared, in an investigation already drawing political scrutiny.
Osterholm, who I am convinced may be clairvoyant, made this
argument in the New England Journal of Medicine in 1997, after Texas and
Houston officials named California strawberries in a cyclosporiasis cluster
that turned out to be tied to Guatemalan raspberries. The obligation to warn
people is real, he wrote, and it has to be weighed against a cost of being
wrong that gets paid twice: once by whoever was falsely accused, and again by
every future warning the public quietly stops believing. He published the same
argument again in 1999,
under the title "Lessons Learned Again," after the outbreak repeated.
That second cost is not abstract. It looks like people who
stop buying lettuce of any kind for the rest of the summer, growers who lose a
season over it, and someone scrolling past the next recall notice because the
last one seemed to get walked back. It also looks like a public that can no
longer tell the difference between a point-source outbreak (in which illnesses
are traced to a common food source) and the ordinary seasonal background of a
reportable disease, which means every summer from here on starts to feel like
an emergency.
Two right answers, one message
There were two right answers here, and only one message
going out. For someone on chemotherapy or living with a transplant,
cyclosporiasis isn't a rough week. It runs longer, relapses, and brings
complications that need real clinical attention. Telling that person to skip
lettuce entirely while the source was still unknown was good advice.
For most of the country, though, it wasn't. Craig Hedberg,
PhD, at the University of Minnesota, has been making
that case all month, and he is right that broad avoidance guidance
without a known source does more harm than good. Getting both messages out at
once means deciding who you are talking to and saying so plainly.
The detective work in this outbreak happened in state health
departments, and it was good. Hedberg has described what happens next: States
recognize increases well before the data are compiled federally into anything
officials can act on.
What it leaves behind is a patchwork whereby some states
monitor effectively and others can't, which doesn't work for a product grown on
many farms, mixed at a central processor, and shipped everywhere.
That delay is not inevitable, but it is getting harder to
avoid. Someone has to gather, standardize, and assemble what the states are
finding, and researchers at Johns Hopkins have documented the erosion of
the federal food safety staffing, funding, and enforcement that that work
depends on. What it leaves behind is a patchwork whereby some states monitor
effectively and others can't, which doesn't work for a product grown on many
farms, mixed at a central processor, and shipped everywhere.
Everyone working this outbreak has been doing the best they
can with a patchwork of information, in front of a public that is
understandably worried and asking every day what is safe to eat.
Nuance and details matter a whole lot here, and all of it
got flattened into a single rising number. A beat to step back and take the
10,000-foot view would have gotten us communication that was more streamlined,
more accurate, and far more useful to the people trying to figure out what to
feed their families.
Dr. Steier is a public health scientist and scientific
communicator. She is the founder of Unbiased Science,
an organization that uses data visualizations, real-world analogies, and human
voice to communicate complex scientific concepts for public understanding via
multiple media modalities.
The opinions voiced in CIDRAP Op-Ed pieces are the
authors' own and do not necessarily represent the official position of CIDRAP.
