WASHINGTON – Four Defense Department workers have been put in post-exposure treatment, a defense official said, following the revelation the U.S. military inadvertently shipped live anthrax samples in the past several days.

CNN learned on Wednesday a Maryland-based lab received the live samples, which prompted an across the board urgent review to see whether any other live anthrax has been shipped.

Officials are concerned because samples left over at the lab in Dugway, Utah, where the samples originated, were tested and determined to contain live agent.

The shipments, thought to be dead, were shipped under less rigorous conditions than the live agent protocol.

Science experts told the Defense Department there was no risk to the public from shipping in those containers. However, four workers across the nine states that received the shipments have been put on post-exposure treatment, because they handled samples.

Pentagon spokesman, Col. Steve Warren, said one sample was also sent to the Joint United States Forces Korea Portal and Integrated Threat Recognition Program at Osan Air Base.

“No personnel have shown any signs of possible exposure. The sample was destroyed in accordance with appropriate protocols,” Warren said.

Up to 22 people in a training laboratory were exposed, according to a statement from the base.

“All personnel were provided appropriate medical precautionary measures to include examinations, antibiotics and in some instances, vaccinations,” the statement said. “None of the personnel have shown any signs of possible exposure.”

The facility was decontaminated afterward and the anthrax destroyed.

Samples are supposed to be rendered dead before they are shipped under a routine research program. All military, government and commercial labs that may have received samples are now reviewing their inventory of anthrax.

The Centers for Disease Control and Prevention is investigating in conjunction with the Defense Department and said they do not suspect any risk to the public.

“CDC is working in conjunction with state and federal partners to conduct an investigation with all the labs that received samples from the DOD,” Jason McDonald, a CDC spokesman said. “The ongoing investigation includes determining if the labs also received other live samples, epidemiologic consultation, worker safety review, laboratory analysis and handling of laboratory waste.”

A military spokesman confirmed there is no known public risk nor any illnesses reported.

“The DOD lab was working as part of a DOD effort to develop a field-based test to identify biological threats in the environment,” said Warren, the department spokesman. “Out of an abundance of caution, DOD has stopped the shipment of this material from its labs pending completion of the investigation.”

The investigation began after a request from a private commercial lab.

“The lab was working as part of a DOD effort to develop a new diagnostic test to identify biological threats,” McDonald said. “Although an inactivated agent was expected, the lab reported they were able to grow live Bacillus anthracis (anthrax).”

The CDC has sent officials to the military labs to conduct on-site investigations, he said.