The logic makes
sense to me. Sewage treatment is not perfect, and pathogens can be difficult to
eradicate entirely. Some can survive, and when that treated water is used to
irrigate crops, it can provide a plausible route for food contamination. It is
emerging as one of the most plausible sources, according to Joan Rose, a public
health water microbiologist who studies pathogens found in sewage, in an
article in The Conversation.
“Cyclospora is found only in humans, where it replicates
in the intestinal tract, causing severe diarrhea. The organism reproduces by
releasing oocysts, which are excreted in those human feces.”
Some of the oocysts can
survive in treated sewage effluent after it enters local waterways, especially
in warm temperatures. If those waters are used to irrigate crops, the oocysts
can be transported on the crops all the way to the grocery store. Rose studied
cyclospora during the first documented outbreak in the U.S. in 1995 in Florida,
where 45 cases were reported. Little was known about Cyclospora at the time. In
that case and a few others in 1996 and 1997, the cause was determined to be
contaminated raspberries from Guatemala. The current outbreak has sickened
22,000 people and killed two people in Michigan.
“It is not easy to measure cyclospora oocysts in sewage,
contaminated water or food. Even modern laboratory methods have trouble
reliably detecting low levels of oocysts, which can still cause disease.”
“Cyclospora oocysts have been found in sewage around the
world. A range of studies across the world shows that they can be detected in
up to 25 percent of sewage samples — but not all studies report how high or low
the concentrations of the oocysts were. So it can be hard to say exactly how
widespread it is.”
“A person who is infected with cyclospora excretes 100
to 10,000 oocysts per gram of feces for as long as 60 days. Based on what is
known about other fecal pathogen excretions from patients, related to the
concentrations of those pathogens in sewage, I estimate that there could be
from 1 to 100 oocysts per liter in sewage.”
Rose currently works in a
laboratory at Michigan State University, where they are trying to develop a
method to more accurately detect this parasite even at lower levels in sewage.
She thinks that wastewater surveillance can be used to know when an outbreak is
growing or subsiding, as it does during COVID outbreaks. She also cites work on
other protozoan pathogens such as Cryptosporidium and Giardia. The oocysts
produced by Giardia are the same size, and those produced by Cryptosporidium
are about half the size of those of cyclosporiasis. During a study in 2001-
2003, they found those two protozoa in treated sewage at six sewage treatment
plants, and some of that water had been approved for non-potable uses,
including for crop irrigation. Chlorination, commonly used for wastewater
treatment, does not kill all of these protozoan oocysts. It is suspected that
those oocysts that make it past treatment can survive for months during warmer
seasons in the environment.
She notes that in the U.S.,
around 200 billion gallons of treated wastewater are used to irrigate crops. A
portion of that water does undergo additional treatment, filtration, and
disinfection.
She notes that there are
available methods to treat protozoa more specifically, such as UV light, which
is used at many sewage treatment plants, and specialized filtration:
“Filtration can remove protozoa but must be designed and
operated correctly. Chlorination is not effective, but ultraviolet light does
inactivate cryptosporidium and eimeria, a chicken protozoan highly related to
cyclospora and used as a surrogate in studies testing methods of killing
cyclospora by the food safety industry.”
Hot weather speeds up the
maturation cycle of cyclosporiasis. Below is a section from the John Hopkins
Bloomberg School of Public Health about how cyclosporiasis spreads.
U.S. food safety regulations
rely on a method known as Hazard Analysis Critical Control
Points (HACCP), which is explained below.
“The U.S. has long relied on an approach called Hazard
Analysis Critical Control Points (HACCP), originally developed in the late
1950s by NASA and Pillsbury to keep astronauts from getting food poisoning in
zero gravity. HACCP maps out every point “from farm to fork, those key choke
points” where contamination could occur, and builds in monitoring and a “stop”
mechanism when something goes wrong, Schwab says. It works—but only when it’s
actively maintained, reported, and enforced.”
“According to Schwab, the enforcement piece is what has
eroded. Federal agencies have lost staff and funding needed to inspect, audit,
and monitor food producers, leaving more of the system dependent on voluntary
industry self-regulation.”
“Self-regulation works until it doesn’t,” Schwab says.
That’s where FoodNet came in. FoodNet is the joint CDC-FDA-USDA-EPA active
surveillance system that tracks foodborne illness across 10 sentinel sites.
Cyclospora reporting was mandatory until July 2025 when the Trump
administration made reporting optional for Cyclospora, along with five other
pathogens (Campylobacter, Listeria, Shigella, Vibrio, and Yersinia).
Thus, deregulation in the
food safety sector leads to vulnerabilities, in this case, especially
deregulation that reduces wastewater surveillance efforts. It can help with
early detection, find sources faster, and lead to less severe outbreaks.
As noted below, the key to
prevention and minimization of the severity and extent of outbreaks is robust
wastewater surveillance.
“Restoring surveillance capacity, Schwab argues, is the
central fix: a fully funded, fully staffed federal system with mandatory
pathogen reporting so that multistate patterns are identified within days
rather than after an outbreak has already spread nationwide. States that have
kept investing in their own monitoring show what’s possible, but a
state-by-state patchwork can’t substitute for a coordinated federal response,
particularly for products that cross state lines.”
“It’s critical to ensure that there are strict controls
on irrigation water, and on-farm sanitation practices can minimize risks, says
Love: “Are farm workers given time to go to the bathroom? Are bathrooms
provided to them? Do they have a handwashing station with warm water? That gets
back to, you know, how do you treat your workers?”
References:
I
study pathogens in sewage. Here's how cyclospora could be getting into our
food. Joan Rose| The Conversation.
Washington Post. August 9, 2026. I study pathogens in sewage. Here's
how cyclospora could be getting into our food.
‘We
Had It Coming’: Cyclosporiasis Outbreak Reveals Holes in Food Safety System: How
gaps in surveillance allowed a hardy foodborne parasite to reach thousands of
Americans. Annalies
Winny. John Hopkins Bloomberg School of Public Health. July 22, 2026. Understanding
the Cyclosporiasis Outbreak | Johns Hopkins | Bloomberg School of Public Health
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