WASHINGTON — U.S. health authorities have widened an investigation into a growing Cyclospora outbreak potentially associated with iceberg lettuce sourced from central Mexico.

The FDA and CDC have identified cases across 15 states, adding six states to the investigation as officials work to determine how the parasite entered the food supply.

Cyclospora is a parasite that can cause gastrointestinal illness, including prolonged diarrhea and other digestive symptoms.

The investigation has focused attention on the safety of fresh produce and food distribution networks, while health officials continue working with state agencies and industry partners.

The outbreak comes after suppliers previously removed certain iceberg lettuce from the market in response to information from federal health authorities.

The expanding investigation highlights the importance of food-safety monitoring and rapid outbreak detection as U.S. health agencies work to identify potentially contaminated products.