A new complication has emerged in the investigation into the cyclospora outbreak tied to lettuce, creating fresh uncertainty around a food-safety case that has reportedly sickened thousands of people in the United States. The development marks a setback for federal investigators trying to determine exactly where the contamination originated.

According to the available details, Mexico’s health minister has pushed back against the U.S. Food and Drug Administration’s approach to the case. That response could make it harder for officials to build a clear account of how the outbreak spread and whether imported produce was responsible.

The dispute matters because cyclosporiasis cases linked to leafy greens can be difficult to trace with precision, especially when products move through complex supply chains. Any disagreement between U.S. and Mexican authorities may slow efforts to confirm the source and narrow down responsibility.

For now, the lettuce-linked cyclospora probe appears to be entering a more contested phase. With questions still unresolved, the latest turn suggests the investigation may take longer to produce firm conclusions about the outbreak and the path of contamination.