Travellers heading to the US this summer are being advised to pay extra attention to food and water hygiene as health officials investigate a rapidly growing outbreak of cyclosporiasis, a foodborne illness linked to a microscopic parasite.
The US Centers for Disease Control and Prevention (CDC) has confirmed 1,645 cases since 1 May, while more than 5,100 additional cases are under investigation across 34 states. If confirmed, the total would approach 7,000 cases, far exceeding the number reported during the same period last year.
Michigan has recorded the highest number of cases, with more than 3,700 reported by state health officials. Clusters have also been identified in Ohio, West Virginia and Kentucky, with additional cases reported in states including New York, North Carolina, Illinois, Texas, Indiana and New Jersey.
The illness is usually spread through contaminated food or water rather than person-to-person contact. Symptoms include watery diarrhoea, stomach cramps and bloating, and can last for weeks if left untreated. Around one in 11 confirmed patients has required hospital treatment, although no deaths have been reported.
The source of the outbreak remains unknown. While leafy greens and lettuce are among the foods being investigated, authorities have not identified any specific produce, grower, supplier or restaurant responsible.
Tracing the parasite has proved particularly difficult because people typically become ill around a week after infection, making it harder to recall what they ate. Testing fresh produce for the parasite is also more complex than for many other foodborne illnesses.
For travellers, health authorities recommend thoroughly washing fresh produce, drinking safe water and practising good food hygiene while investigations continue.