What is cyclosporiasis? The parasitic illness behind the growing US outbreak

Health officials in the United States are investigating a growing outbreak of cyclospora, a foodborne parasite that causes cyclosporiasis, an intestinal illness known for severe watery diarrhoea that can last for weeks if left untreated.

Cyclosporiasis is caused by the microscopic parasite Cyclospora cayetanensis, which is most commonly spread through contaminated fresh fruit, vegetables or water. Unlike many stomach bugs, the parasite is not usually passed directly from person to person, as it must first mature in the environment before becoming infectious.

Common symptoms include prolonged watery diarrhoea, stomach cramps, nausea, vomiting, bloating, fatigue, loss of appetite and weight loss. Symptoms often appear around a week after exposure and can continue for several weeks without treatment, particularly in people with weakened immune systems.

Health authorities have linked previous outbreaks to contaminated produce including lettuce, basil, cilantro, raspberries and other fresh vegetables. Investigators have not yet identified the source of the current outbreak, which has affected hundreds of people across multiple US states.

Experts recommend thoroughly washing fresh fruit and vegetables, practising good hand hygiene and avoiding untreated water while investigations continue. Most cases can be successfully treated with antibiotics prescribed by a healthcare professional.

While the illness is rarely life-threatening, older adults, young children and people with weakened immune systems are at greater risk of developing more serious complications and should seek medical advice if symptoms persist.