Cyclospora in the Salad Bowl

The United States is experiencing an unusually large outbreak of cyclosporiasis, a prolonged diarrheal illness caused by the microscopic parasite Cyclospora cayetanensis. Although the disease is rarely fatal, it can produce weeks of watery diarrhea, fatigue, anorexia, abdominal distress, volume contraction, and weight loss. Its tendency to disappear briefly and then return makes it particularly unpleasant and sometimes diagnostically confusing.

The immediate focus of the investigation is shredded iceberg lettuce served at certain Taco Bell restaurants in Indiana, Kentucky, Michigan, Ohio, and West Virginia. Epidemiologic and supply-chain evidence led the Centers for Disease Control and Prevention and the Food and Drug Administration to identify lettuce supplied by Taylor Farms de México as the vehicle of infection. The company has removed iceberg lettuce originating in central México from the U.S. market and informed FDA that it would initiate a recall. The investigation remains open, partly because officials are still determining whether the same lettuce reached additional restaurants, retailers, or distributors.

The outbreak in numbers

The national figures cover domestically acquired infections reported since May 1. They are substantially higher than the 249 cases reported nationally by approximately the same point in 2025. The CDC expects the number to rise because case reporting may lag behind the onset of illness by as much as six weeks.

The two columns should not be added together. The FDA describes the five-state restaurant-associated illnesses as a subset of the national surveillance data. Nevertheless, the near identity of the two confirmed case totals is difficult to reconcile completely from the public data, which were prepared at different times and under somewhat different reporting procedures. State totals may also be much higher because states count probable as well as laboratory-confirmed cases.

Among 190 affected people in Michigan who reported eating at Taco Bell, 90 percent recalled eating iceberg lettuce. Traceback investigations then converged on Taylor Farms de México, which supplied shredded lettuce to restaurants at which patients had eaten. That combination of a striking epidemiologic association and a common supply source is powerful evidence. However, investigators have not yet publicly identified the precise farm, water source, processing step, or sanitation failure at which contamination occurred.

A parasite that must mature before it can infect

Cyclospora behaves differently from most organisms that produce acute gastroenteritis. An infected person excretes microscopic oocysts in the stool, but those newly excreted oocysts are not immediately infectious. They must spend days or weeks in the environment before maturing, or “sporulating,” into an infectious form. Consequently, cyclosporiasis is not ordinarily passed directly from one person to another in the manner of norovirus or shigellosis.

The basic transmission cycle can be represented as follows:

Infected person
      │
      ▼
Oocysts passed in stool
—not yet infectious—
      │
      ▼
Days or weeks in water, soil
or another suitable environment
      │
      ▼
Oocysts become infectious
      │
      ▼
Contaminated irrigation water,
wash water or food-contact surfaces
      │
      ▼
Fresh produce contaminated
      │
      ▼
Produce eaten raw
      │
      ▼
Parasite infects the small intestine
      │
      ▼
Watery, sometimes relapsing diarrhea

This environmental maturation explains why outbreaks are so often associated with fresh produce rather than with direct household transmission. Lettuce, herbs and berries may be eaten raw, have complex surfaces on which organisms can lodge, and may pass through numerous farms, processing plants, distributors and kitchens before reaching the consumer. Previous U.S. outbreaks have involved leafy greens, bagged salads, basil, cilantro, parsley, raspberries, snow peas and other produce.

Why the disease is easily missed

Symptoms usually begin about one week after contaminated food is eaten, although the interval may range from two days to two weeks or longer. The delay makes food histories difficult. By the time diarrhea begins, a patient may have eaten in several restaurants and consumed many salads, garnishes and prepared foods.

The characteristic illness is frequent watery diarrhea. It may be accompanied by cramping, bloating, excess gas, nausea, anorexia, fatigue, low-grade fever, and sometimes vomiting. Weight loss can become substantial when the illness continues. Untreated symptoms may persist for a month or longer and often follow a remitting-relapsing course: the patient improves, assumes the illness is over, and then develops diarrhea again.

Cyclosporiasis may also escape diagnosis because an ordinary stool culture does not detect the parasite. Even a routine examination for ova and parasites may fail unless the laboratory is specifically asked to look for Cyclospora. Diagnosis can be made with a molecular gastrointestinal panel or by special microscopic techniques, including modified acid-fast staining and ultraviolet fluorescence. The CDC has consequently advised clinicians to request Cyclospora testing specifically in patients with compatible persistent or relapsing diarrhea.

This is especially important during an outbreak. A patient may initially be labeled as having viral gastroenteritis, food intolerance, medication-related diarrhea or nonspecific “food poisoning.” Because some people recover without seeking care and others are never tested, the official total almost certainly understates the true number infected.

Treatment and prognosis

The treatment of choice is trimethoprim-sulfamethoxazole, commonly known as TMP-SMX or Bactrim. Most otherwise healthy people will eventually recover without treatment, but treatment usually shortens an illness that might otherwise continue or relapse for weeks. Patients with impaired immunity may require a longer course. Unfortunately, no comparably effective alternative has been established for people who cannot take sulfonamides, making accurate diagnosis and individualized medical management particularly important in that group.

The absence of reported deaths is reassuring, but it should not lead to dismissal of the illness as trivial. Persistent diarrhea can cause volume contraction, electrolyte disturbances, malabsorption, and significant weight loss. Older adults, young children, and people with weakened immune systems are more likely to become seriously ill or require hospitalization. The CDC has also listed less common complications such as cholecystitis and reactive arthritis.

Anyone with persistent watery diarrhea – particularly after eating at an implicated restaurant – should contact a healthcare provider, maintain fluid intake, and mention the possibility of cyclosporiasis. Signs such as dizziness, reduced urination, profound weakness, confusion, inability to keep fluids down, or worsening illness warrant prompt medical evaluation.

What consumers should do

The present warning is targeted, rather than a recommendation to abandon all salads everywhere. The CDC and the FDA advise against eating food containing shredded iceberg lettuce from Taylor Farms de México served at Taco Bell locations in the five named states. Leftovers containing the implicated lettuce should be discarded, and containers or surfaces that contacted it should be cleaned. The specific restaurant advisory does not presently include Texas, although other, apparently unrelated Cyclospora clusters remain under investigation nationally.

Fresh produce should be rinsed thoroughly under running water, and outer leaves of lettuce or cabbage should be discarded. Hands, knives, cutting boards, and work surfaces should be cleaned to prevent cross-contamination. These measures reduce risk, but cannot guarantee removal of Cyclospora, especially when the organism is lodged in folds or crevices. Cooking is more reliable: The CDC states that heating produce to at least 158°F, or 70°C, kills the parasite. That advice is more practical for vegetables normally served cooked than for lettuce.

The broader lesson

This outbreak demonstrates both the strengths and limitations of modern foodborne-disease surveillance. Molecular testing, detailed patient interviews and supply-chain traceback have allowed investigators to connect illnesses occurring across several states with one ingredient and one supplier. Yet the long incubation period, intermittent symptoms, underdiagnosis, complex produce-distribution system and delays in reporting mean that recognition still comes weeks after the first people become ill.

It also illustrates why fresh produce presents a special food-safety challenge. Meat can be cooked, milk can be pasteurized and canned food can be sterilized. Lettuce is expected to arrive crisp, uncooked and ready to eat. Once microscopic fecal contamination enters its production chain, there may be no final “kill step” before the product reaches the table.

The practical response is neither panic nor complacency. The implicated lettuce should be avoided, persistent diarrhea should be investigated rather than merely endured, and official advisories should be followed as the traceback expands or contracts. The outbreak is large, but it is identifiable, treatable, and – once the contaminated food is removed – controllable.