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After months of widespread transmission that impacted dozens of U.S. states and left thousands of people ill, the largest recorded cyclospora outbreak in modern U.S. history has officially come to an end, U.S. Centers for Disease Control and Prevention (CDC) officials announced Friday.

The parasitic intestinal infection, which causes severe, explosive diarrhea, has been linked to two deaths in Michigan and hospitalized 570 people since the outbreak began earlier this year. Both of the deceased individuals had serious pre-existing underlying health conditions that left them more vulnerable to complications from the infection and related dehydration, Michigan health authorities confirmed. While cyclospora infections are rarely fatal for otherwise healthy people, the outbreak’s scale and impact have drawn widespread public attention and public health intervention.

Investigators have traced the majority of confirmed cases to contaminated lettuce imported from central Mexico by produce supplier Taylor Farms, which distributes fresh leafy greens to countless food retailers and restaurant chains across the United States. Following the link being established, Taylor Farms issued a voluntary nationwide recall of all lettuce sourced from its central Mexican growing operations, and major fast-food chain Taco Bell moved quickly to remove the supplier’s lettuce from all menu items to limit further exposure.

CDC data shows that as of early September, nearly 20,000 confirmed cyclospora cases have been reported across all 49 U.S. states and the District of Columbia since May 1, with total hospitalizations topping 1,000. Of that total, more than 12,000 cases were tied to the multi-state outbreak linked to the Mexican lettuce. Public health experts emphasize that the true number of infections is almost certainly far higher than the confirmed count, as many mild cases go unreported by patients who do not seek medical care. It is also important to note that while the majority of cases were connected to the contaminated lettuce, thousands of reported illnesses have not yet been linked to that source.

In its official advisory declaring the outbreak over, the CDC stated that new case counts have dropped significantly after the recall and menu changes. However, agency officials added that investigations into the full origin and spread of the parasite will continue to help prevent similar large-scale outbreaks in the future.

This outbreak marks a stark increase in cyclospora cases compared to previous years. Prior to 2025, the worst year for cyclospora infections in the U.S. was 2019, when just 4,700 cases were recorded nationwide. Beyond U.S. borders, public health officials in the United Kingdom have also issued warnings to travelers after multiple returning UK residents contracted the parasite during trips to the U.S. this year.

Cyclospora is a microscopic parasite that spreads exclusively through contaminated food or water. Infection, called cyclosporiasis, most commonly causes severe intestinal distress including the explosive diarrhea that has become synonymous with this outbreak, and can lead to dehydration if left untreated.

Against the backdrop of increasingly destructive wildfires raging across the American West, a growing divide has emerged over an untested alternative treatment that hundreds of firefighters have turned to ease smoke-related health symptoms: inhaled glutathione.

For veteran Pasadena Fire Captain David Marquez, the solution came just days after he helped battle the devastating Eaton Fire, a blaze that etched its place as the second most destructive in California history, leaving 17 dead and more than 9,000 structures reduced to ash. Standing on the shoulder of a road outside Pasadena’s Rose Bowl Stadium, Marquez inhaled his first dose of the antioxidant, months after he and his crew had been reeling from persistent post-fire health issues. “We were having trouble sleeping, dealing with chronic coughs, headaches, crippling fatigue — it was just a really rough set of symptoms after the fire,” Marquez explained in recent testimony. The 25-year firefighting veteran said relief was almost immediate, even after what he calls the worst toxic exposure of his career. With crew members desperate for any reprieve from their debilitating symptoms, “we were willing to try pretty much anything,” he added.

Marquez’s experience is far from unique. For years, public health researchers have confirmed that repeated inhalation of toxic wildfire smoke puts first responders like firefighters at drastically elevated risk of long-term illness, including multiple forms of cancer. Data from the U.S. National Institute for Occupational Health and Safety puts that risk in concrete terms: firefighters face a 14% higher chance of dying from cancer than the general American public. As awareness of these occupational hazards has grown over the past decade, so too has interest in unproven, sometimes risky alternative interventions that promise to mitigate damage after fire exposure.

Glutathione, an antioxidant produced naturally in the human body, has been offered as an on-site treatment by volunteer groups at many of the largest U.S. wildfires in recent years, from last summer’s blazes near Spokane, Washington, to earlier outbreaks across Northern California. Anecdotal accounts from frontline clinicians and fire department crews have offered encouraging early signals: many users report rapid relief from common post-exposure symptoms, and some proponents claim it helps flush carcinogenic toxins absorbed through smoke inhalation out of the body. But to date, no large-scale, peer-reviewed clinical research has confirmed its safety or effectiveness for this use, and public health and firefighter advocates have raised serious alarms about supply contamination, unregulated dosing, and the risks of promoting an untested treatment to vulnerable workers.

Last month, the International Association of Fire Fighters (IAFF), which represents more than 360,000 active and retired firefighters across the U.S. and Canada, issued a rare public warning about the growing unregulated use of inhaled glutathione. The organization highlighted two recent product recalls linked to contaminants at compounding pharmacies that produce the injectable and inhalable versions of the supplement. While the association stressed that past scares involving naturally occurring vitamins that ended up increasing cancer risk are not directly tied to glutathione, the case underscores the danger of rolling out untested treatments to at-risk workers.

“We don’t know if glutathione actually delivers on the benefits its proponents claim,” said Sean DeCrane, assistant to the IAFF general president for health and safety. “We don’t know if the reported improvements are just a placebo effect, and we have no data on the long-term health impacts of regular inhaled use.” DeCrane criticized the aggressive promotion of glutathione to frontline crews, pointing to incidents in Spokane where fire chiefs included recommendations for crews to visit volunteer treatment tents during morning briefing sessions. “The total lack of rigorous research is what really raised red flags for our organization,” he said, adding that the IAFF has already heard from multiple members who reported feeling worse, not better, after receiving glutathione treatment. In many of those cases, DeCrane said, treating clinicians told users their worsening symptoms were just a sign that toxins were being flushed from their bodies.

The current push to bring glutathione treatment to wildfire crews traces its origins back to 2017, when a group of naturopathic practitioners banded together in Santa Rosa, California, to offer support to crews battling the destructive Tubbs Fire. That initial effort grew into the Integrated Health Action Network (IHAN), previously known as the Integrative Healers Network, which now deploys volunteer clinicians to major wildfire events across the country to provide glutathione alongside other complementary treatments including acupuncture and massage therapy.

In response to the IAFF’s warning, IHAN released a statement acknowledging the critical need for further formal research, and said the organization is eager to partner with academic researchers to generate rigorous data on glutathione’s effectiveness. Jen Riegle, a licensed naturopath and IHAN co-founder, noted that the group’s treatment has consistently led to what she calls “clinically meaningful improvements” in the most common post-fire symptoms: headaches, fatigue, and brain fog that leave crews unable to work effectively. Riegle stands by the claim that glutathione helps eliminate harmful contaminants from firefighters’ bodies, and acknowledged that mild short-term side effects are common immediately after treatment.

Riegle said she hopes the anecdotal data her group has collected over nearly a decade of work will help secure funding and support for large-scale clinical trials to confirm the treatment’s value, with the goal of making it a standard long-term health intervention for firefighters. At the same time, she emphasized that the group’s current evidence is entirely anecdotal, and far from the conclusive data required for formal regulatory approval. “I want to be really clear that what we are collecting is program-level data from our treatment work,” she said. “It shouldn’t ever be misconstrued as clinical trial data, double-blind placebo-controlled data, or peer-reviewed research. It’s just a starting point to build support for future formal studies.” It is important to note that full clinical trials for new medical interventions typically take years of rigorous testing and evaluation before winning regulatory approval.

The debate over glutathione burst into the public sphere last year, when California’s State Board of Pharmacy proposed new rules that would have severely restricted compounded production of the supplement. The proposal sparked a massive wave of pushback from firefighters across the state, who traveled to Sacramento to testify in person about the improvements they had experienced after using the treatment. The board ultimately abandoned the proposed restrictions. Marquez was among the uniformed firefighters who traveled to the capital to testify, and he said he is grateful that glutathione is now more widely available to crews, including at every fire station in his home city of Pasadena. He dismisses critics who argue that his reported improvement is nothing more than a placebo effect. “I don’t care if it’s a placebo — it worked,” he said. “Guys were saying they felt better, I felt better, and that made me want to keep accessing the treatment.”

The debate over glutathione also highlights a longstanding gap between emerging understanding of occupational risks for firefighters and regulatory protection that matches that knowledge. As recently as last year, U.S. National Forest Service firefighters were banned from wearing protective face masks on the job over unfounded concerns that the gear would impair their ability to operate in rugged mountain terrain. Today, there is a growing consensus across the fire service that improved respiratory protection and routine decontamination are critical to reducing the elevated cancer risk that comes with the job.

Dr. Coralynn Sack, an occupational pulmonologist at the University of Washington who specializes in the health impacts of air pollution, confirmed that wildfire smoke is a well-documented inhalational hazard that causes lasting damage to first responders. “There’s been a lot of broad interest in using antioxidant supplements to mitigate damage from air pollution overall, but studies have returned very mixed results — some have even found that antioxidant use leads to worse health outcomes,” Sack explained. While Sack said there is biological plausibility to the idea that glutathione could reduce smoke-related damage, she added that she is “very underwhelmed by the existing data” to support its use for firefighters. No peer-reviewed clinical trials of inhaled glutathione for firefighter smoke exposure have ever been completed, she noted. What’s more, Sack argued that the current debate over glutathione distracts from proven, evidence-based interventions that are already known to reduce risk, like widespread access to high-quality personal protective equipment.

For Greg Fonts, a fire captain in West Sacramento and vice president of his local IAFF chapter, the growing conversation around glutathione is part of a much larger shift in fire service culture around occupational health. Gone are the days, he said, when firefighters would leave ash caked on their helmets and jackets to brag about the blazes they had fought, and write off cancer as an unavoidable part of the job. “When I joined the fire service in 2000, that was the prevailing attitude: cancer was just something that came with the work,” Fonts, who has used glutathione himself, explained. “The culture has changed drastically. Younger firefighters take their long-term health way more seriously now, and that’s a good thing.”