A US outbreak of cyclosporiasis, a parasitic infection that can cause severe diarrhoea, has prompted widespread concern on social media, where people are comparing symptoms and worrying they may be infected. The attention matters because online discussion may raise awareness of an under-tested illness, but it can also amplify anxiety among people whose symptoms may have other causes, such as irritable bowel syndrome.

The CDC estimates that nearly 7,000 people may have been affected nationwide, though the true total is likely higher; Michigan alone had reported 4,312 cases at publication. State health authorities have identified lettuce or salad greens as possible sources, but have not named a specific ingredient, grower or supplier; previous outbreaks have been linked to leafy greens, herbs and raspberries. Diagnosis is difficult because routine stool tests do not usually check for cyclospora and many people with diarrhoea do not seek medical care.