Public-health officials declared an end to a cyclosporiasis outbreak linked to iceberg lettuce that spread across the U.S. this summer.

The outbreak has resulted in a total of 12,883 reported cases of the gastrointestinal food-borne illness across 21 states, the Centers for Disease Control and Prevention said Friday.

Federal health officials have linked the outbreak to shredded iceberg lettuce from Taylor Farms, a major supplier of fresh produce to retailers such as Walmart, Costco Wholesale and Amazon.com's Whole Foods Market, as well as restaurant chains including McDonald's and Yum Brands' Taco Bell.

The CDC said the contaminated lettuce linked to the outbreak is no longer available in stores or restaurants, and the products' best-by dates have passed. Recent infections linked to the outbreak have declined, with fewer than two infections per day on average in August compared to a peak of more than 1,000 daily infections, the CDC said.

Health authorities had linked the outbreak to lettuce served at some Taco Bell locations in July, making the Mexican-style chain a key focus of consumers' concerns. The company said it voluntarily removed lettuce supplied by Taylor Farms within 72 hours of public-health officials notifying the chain about a link between the produce and the outbreak.

The Food and Drug Administration said it continues to investigate how the product linked to the outbreak became contaminated with cyclospora, the parasite that causes cyclosporiasis.

Cyclosporiasis is characterized by explosive diarrhea, and can also cause stomach cramps, nausea and other symptoms.

Taylor Farms said its facility in central Mexico remains closed as the company, the FDA and independent experts complete their investigations. "We will have more information to share at that time," a spokesperson for the company said.