US health officials have identified lettuce served at Taco Bell restaurants across five states as one of the sources of a widespread outbreak of the diarrhoea-causing parasite cyclospora.The US Centers for Disease Control and Prevention (CDC) issued a warning to consumers on Thursday evening, local time, warning them not to eat shredded iceberg lettuce from Taco Bell in Indiana, Kentucky, Michigan, Ohio and West Virginia.A record number of cyclospora cases have been reported in more than 30 US states, and experts have said not every illness is likely to have been caused by a single source.A Food and Drug Administration (FDA) investigation has so far identified just one supplier of lettuce as a source of the outbreak, and the FDA is working with that supplier to determine if any "potentially contaminated shredded iceberg lettuce remains on the market", according to the CDC."Taco Bell has committed to stop using any lettuce from the supplier identified by the FDA's traceback investigation," the statement added.While the federal warnings to consumers did not identify the company, Taylor Fresh Foods, of Salinas, California, said FDA testing indicated it was "a specific independent farm" in Mexico affiliated with the company that appeared to be the problem.Taylor Farms has been tied to foodborne outbreaks in the past, including a 2013 cyclosporiasis outbreak linked to salad mix, and a 2024 E. coli outbreak tied to onions served at McDonald's.Taylor Farms said in a statement on Friday that it was voluntarily removing all iceberg lettuce sourced from central Mexico from the US market."As a family-owned and -operated company, we are deeply concerned for those who became ill, their families, and the many Americans whose trust in the safety of their fresh produce has been shaken," the statement said.Outbreak surpasses previous case peakCyclospora is a microscopic, spherical parasite that commonly causes watery diarrhoea "with frequent and sometimes explosive bowel movements", according to the CDC.The heat-loving parasite infects the bowels and spreads through faeces. In the past, people have been infected by consuming fruits or vegetables that were exposed to faeces-contaminated irrigation water.The illness it causes, called cyclosporiasis, is not usually life-threatening and is typically treated with antibiotics.Many cases are never linked to a specific food or other source, and for years few US cyclospora outbreaks were reported.But the number started rising about a decade ago, with a particularly notable spike in 2019, when 4,700 cases were reported.The current surge has far surpassed that.Michigan, the apparent epicentre of the current outbreak, is reporting more than 5,000 cases, including about 100 hospitalisations.More than 2,000 additional probable and suspected cases have also been reported in other states.Climate change, better detection behind riseExperts attribute the increasing trend in cases to climate change and better detection.They also say it is likely that cyclospora cases were historically under-reported, for several reasons.Some common tests used to check for food poisoning have not been geared to detect cyclospora, for example.Technicians are also unable to grow the parasite in labs, making it hard to draw evidence from contaminated produce.It can also be hard to figure out what food sick people had in common because sometimes it is a single ingredient that might be common in multiple recipes, such as basil or coriander.In North Carolina, where the outbreak has now surpassed 300 cases, authorities said the most commonly reported foods consumed before people fell ill included parsley, coriander and lettuce.However, it is not clear if those ingredients were the source of the infections, they added, and the outbreak did not appear to be linked to Taco Bell in that state.Many of the ill people in Michigan also said they did not eat at Taco Bell, state health officials said on Friday.AP/ABC