More than two-thirds of the 31 laboratory technicians taking preventive medicine for anthrax in the widening Defense Department bio-lab safety failure are Defense Department workers stationed in South Korea.

Pentagon officials said Wednesday that 22 personnel, including active duty, civilian DoD employees and contractors, at Osan Air Base, 30 miles from Seoul, are taking prophylactic measures to safeguard against an infection.

The remainder of what the Pentagon says are 31 people taking prophylactics include one Defense Department laboratory employee in Maryland and seven workers at civilian labs throughout the United States.

Deputy Defense Secretary Robert Work said Wednesday the Pentagon and Centers for Disease Control and Prevention investigations into erroneous shipments of live anthrax from DoD labs in the past few months have has expanded, and have has found that live samples of the virus were shipped to nearly twice as many places as previously thought: 52 labs in 18 states, the District of Columbia, Canada, Australia and South Korea.

Work added that DoD expects the number to rise as more test results are received.

"We are acting with urgency on this matter. All of the testing of these samples is a 'day-on-stay-on' — we are going on it as fast as we can," Work said.

The error was discovered May 22 when a subcontractor to a Maryland laboratory contacted the CDC after cultivating live anthrax from a sample containing supposedly dead spores shipped from the Army's Dugway Proving Grounds in Utah.

But the investigation has shown that bad batches could date back 10 years, according to Navy Cmdr. Franca Jones, medical director for the Pentagon's chemical and biological defense programs.

All the samples that have tested positive originated from Dugway, but the investigation has expanded to examine batches from Fort Detrick, Edgewood Chemical Biological Center and the Naval Medical Research Laboratory, all in Maryland, according to Frank Kendall, undersecretary of defense for acquisition, technology and logistics.

The CDC Centers for Disease Control and Prevention and the Pentagon are investigating why equipment designed to irradiate and kill the bacteria didn't work and safety measures designed to detect live organisms failed.

The inquiry is the largest biological agent investigation since powdered anthrax was mailed to members of Congress and the media in September 2001, killing five, including several postal workers, and infecting 17 others. The criminal investigation eventually traced the anthrax to Fort Detrick.

The officials said there is "zero" risk to the general public or anyone who handled the shipments, adding that the anthrax – which was contained as a liquid in vials -- was too low a concentration to infect a healthy person.

Dried anthrax that can be inhaled is considered to be more lethal than anthrax contained in liquid.

According to the Pentagon, labs in the following states received the shipments of live anthrax: California, Delaware, Maryland, Massachusetts, New Jersey, New York, Rhode Island, Tennessee, Texas, Utah, Virginia, Washington, Wisconsin, Arizona, Florida, Illinois, Ohio and North Carolina.

The Pentagon has not released the names of the labs that received live anthrax; it is reviewing 400 shipments.

Jones said more than 300 labs worldwide are authorized to work with anthrax; the DoD runs nine of these.

Anthrax is largely used in laboratories to develop equipment and tests to identify biological threats and conduct research into vaccines and treatments.

Work said the investigation has found no evidence that the release of live anthrax samples was the result of a "deliberate act." He promised transparency in the investigation and said DoD has established a web site that will be updated with information as more results are known.