Largest Cyclospora Outbreak in U.S. History Spreads Across 45 States as Thousands Fall Ill and Health Officials Scramble to Trace the Source

Health authorities in the United States are investigating what has become the largest recorded Cyclospora outbreak in the country’s history, with thousands of confirmed infections reported across dozens of states and public health agencies working urgently to identify and remove contaminated food products from circulation. The outbreak has already resulted in hospitalisations and the first reported deaths linked to the parasite, prompting renewed concerns about food safety and produce supply chains.

Cyclospora is a microscopic parasite that causes cyclosporiasis, an intestinal illness typically spread through food or water contaminated with human waste. Unlike many foodborne illnesses, symptoms often take about a week to appear after exposure, making outbreaks difficult to detect and trace. People infected commonly experience prolonged watery diarrhoea, stomach cramps, nausea, fatigue, loss of appetite and weight loss. While most healthy individuals recover with treatment, the illness can be particularly serious for older adults, young children and people with weakened immune systems.

According to the U.S. Centers for Disease Control and Prevention (CDC), laboratory-confirmed cases have risen sharply since May, while thousands of additional suspected infections remain under investigation. The outbreak has affected 45 states, with a separate food-tracing investigation linking one major cluster to contaminated shredded iceberg lettuce distributed to 15 states. Federal investigators believe the contaminated produce originated from central Mexico, leading to recalls of affected products as the investigation continues.

Michigan has recorded the highest number of cases, accounting for a significant share of confirmed infections nationwide. State health officials also announced the first two deaths associated with the outbreak, although both individuals reportedly had serious underlying medical conditions. Hundreds of patients have required hospital treatment as public health authorities continue monitoring the spread.

Food safety experts say Cyclospora outbreaks are most common during the warmer months because the parasite is frequently associated with fresh fruits, leafy vegetables and herbs that are eaten raw. Produce such as lettuce, cilantro, basil and parsley has been linked to previous outbreaks in North America, making tracing the exact source especially challenging due to complex international supply chains.

The current outbreak has once again highlighted the challenges of detecting foodborne parasites. Because Cyclospora cannot spread directly from one person to another under normal circumstances, investigations focus on identifying contaminated food or water sources rather than isolating infected individuals. Health officials have advised consumers to pay close attention to food recall notices and seek medical care if they develop persistent gastrointestinal symptoms after eating fresh produce.

The Food and Drug Administration (FDA) and CDC continue working with state health departments, food distributors and growers to determine whether additional products should be recalled. Investigators are also examining whether multiple food sources may be contributing to the unprecedented number of infections reported this year.

As investigations continue, the outbreak serves as a reminder of the importance of strong food safety systems and rapid disease surveillance. While officials remain confident that the risk can be reduced through recalls and improved traceability, they warn that additional cases may still emerge because of the parasite’s delayed incubation period and the time required to identify contaminated food products.