DALLAS (July 12, 2012)—The U.S. Centers for Disease Control and Prevention says the first known victims of sodium azide poisoning at a public place were hospitalized after they drank tea laced with the chemical at a Dallas-area restaurant two years ago.

Authorities say the toxic industrial chemical was deliberately added to a tea urn at the Potbelly sandwich shop in Richardson when employees weren't looking.

The five victims of the April 2010 poisoning have recovered.

No arrests were ever made.

The CDC said it's "the first detailed report of sodium azide poisonings at a public venue."

Dr. Kurt Kleinschmidt, a UT-Southwestern Medical Center at Dallas toxicologist who investigated the case, says there have been no related incidents.

Chicago-based Potbelly told The Dallas Morning News it has now installed tamper-resistant covers on tea urns.