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Anthrax colonies growing in a dish.

Anthrax colonies growing in a dish.

Centers for Disease Control and Prevention

CDC says 75 workers may have been exposed to anthrax

The U.S. Centers for Disease Control and Prevention (CDC) says that it is treating or monitoring 75 of its Atlanta-based staff members for possible anthrax exposure. The exposure may have occurred earlier this month because “established safety practices were not followed,” the agency said in a press statement released today.

“Out of an abundance of caution, CDC is taking aggressive steps to protect the health of all involved, including providing protective courses of antibiotics for potentially exposed staff,” the agency stated. “Based on most of the potential exposure scenarios, the risk of infection is very low.” Anthrax can be deadly if inhaled, with symptoms usually appearing within a few days or weeks, but widely available antibiotics can prevent illness.

Some of the CDC workers were involved in “inactivating”—or rendering harmless—live samples of Bacillus anthracis bacteria in a biosafety level 3 (BSL3) laboratory for shipment to other CDC laboratories with lower biosafety levels, according to CDC. The samples were intended for studies aimed at developing new ways of detecting anthrax in environmental samples. “However, the lab used a procedure that did not adequately inactivate the samples,” according to the statement.

The potentially infectious samples were then used by three laboratories at CDC’s Roybal campus that were not equipped to handle live anthrax. And between 6 and 13 June, lab workers used procedures that may have “aerosolized” the dangerous spores, making them easier to breathe in, investigators found. “Workers, believing the samples were inactivated, were not wearing adequate personal protective equipment while handling the material,” the agency said.

The unintentional exposure was discovered on 13 June when researchers noticed live anthrax colonies growing on plates used to store and transport the samples. CDC officials then moved to decontaminate potentially contaminated areas and notify workers who had handled the plates. Investigations are continuing, and the “laboratories will be re-opened when safe to operate,” according to the statement. “Given that CDC expert protocols were not followed, disciplinary action(s) will be taken as necessary.”

The incident will bring further scrutiny to CDC and other institutions that work with anthrax and other so-called select agents—dangerous toxins and organisms that are specially regulated by the federal government because of the threat they pose if engineered into a bioweapon, or accidentally escape from a laboratory. Internal whistleblowers have cited a range of problems at CDC’s secure laboratories, and in 2011 the National Academies’ National Research Council reported that select agent laboratories in the United States had 395 events between 2003 and 2009 that could have resulted in exposure to or release of an agent (but they reported just seven infections). Critics of the current select agent system have called for more stringent regulation and a reduction in the number of laboratories handling dangerous agents.

BSL3 laboratories have the second strongest containment and safety features, including special air-handling systems, “glove boxes” that keep samples separate from researchers, and secured laboratories. The most stringent labs, BSL4 laboratories, also often require researchers to wear specialized “moon suits” and breathing gear that prevent potential exposures.