Why lettuce is under scrutiny in the US Cyclospora outbreak and what travellers need to know | Doctor explains

A bag of salad greens is not usually something people associate with a parasitic infection. But in the United States, health officials are investigating an outbreak of Cyclospora infections that has sickened dozens of people, with lettuce and mixed salad greens emerging as the common link among many of the reported cases.

The outbreak, currently under investigation in Michigan, has once again highlighted how fresh produce, especially leafy greens that are eaten raw, can become vehicles for foodborne parasites if contaminated anywhere along the supply chain.

Experts say there is no reason for panic, but the incident serves as an important reminder that even countries with stringent food safety standards remain vulnerable to contamination.

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Why is lettuce being linked to the outbreak?

According to US health authorities, many people who fell ill reported eating lettuce, mixed salad greens and other fresh produce before developing symptoms. Investigators are still tracing the exact source of contamination.

Unlike bacteria such as Salmonella or E. coli, Cyclospora cayetanensis is a microscopic parasite that contaminates food or water exposed to human faecal matter. Because leafy vegetables are often eaten raw, they do not undergo cooking that could help eliminate pathogens.

The parasite has previously been linked to imported herbs, basil, cilantro, raspberries and packaged salads, making fresh produce one of the biggest risk factors.

What is Cyclospora?

Cyclospora is a foodborne parasitic infection that primarily affects the small intestine. Dr Aishwarya R, Consultant – Infectious Diseases at Aster Whitefield Hospitals, Bengaluru, says the infection can cause prolonged gastrointestinal illness.

"Cyclosporiasis infection is caused by a minuscule parasite known as Cyclospora cayetanensis and mostly affects the small intestine. It causes prolonged diarrhoea, abdominal pain, bloating, nausea, fatigue, loss of appetite and weight loss in some cases," she explains.

One feature that distinguishes the infection is that symptoms may disappear and then return repeatedly over several weeks if left untreated.

Although the disease is generally not life-threatening in healthy individuals, it can become more serious in older adults, young children and people with weakened immune systems.

Can it spread from one person to another?

Unlike viral stomach infections, Cyclospora does not spread easily through casual contact.

"The organism needs several days to weeks outside the human body before it becomes infectious," Dr Aishwarya explains.

This means someone returning from an affected country is unlikely to infect family members, friends or fellow travellers simply through day-to-day interactions. Instead, most infections occur after consuming contaminated leafy vegetables, herbs, fresh fruits or untreated water.

What symptoms should you watch for?

Symptoms usually begin about a week after consuming contaminated food and may include:

-Persistent or watery diarrhoea

-Stomach cramps

-Bloating

-Nausea

-Fatigue

-Loss of appetite

-Weight loss

Without treatment, symptoms can recur for weeks or even months.

Should travellers be worried?

Experts say travellers should remain cautious but not alarmed. Dr Aishwarya notes that anyone who develops persistent diarrhoea after international travel, particularly if it keeps returning, should consult a doctor.

Routine stool examinations may not always detect Cyclospora, meaning specialised testing could be required.

"The good news is that the infection can be effectively treated with trimethoprim-sulfamethoxazole," she says.

How can you protect yourself?

While the current outbreak is centred in the US, experts say the lessons apply everywhere, especially as global food trade continues to expand.

Dr Aishwarya recommends:

-Wash lettuce, herbs and fresh fruits thoroughly before eating.

-Avoid consuming raw produce from unhygienic sources.

-Drink safe, clean water, particularly while travelling.

-Maintain good kitchen hygiene to prevent cross-contamination.

-Seek medical attention if diarrhoea persists after travel.

She also stresses the need for stronger global surveillance of foodborne parasites.

"As food imports continue to grow, outbreaks may occur far from where the contamination originally happened. Good agricultural practices, clean irrigation water, hygienic food preparation and washing fresh produce remain the best ways to prevent the disease," she says.

The ongoing investigation in the US serves as a reminder that even foods widely considered healthy, such as fresh salads, require careful handling from farm to plate.