Workers at the US Centers for Disease Control and Prevention in Atlanta, Georgia, accidentally shipped highly dangerous H5N1 influenza virus to another government laboratory in March, the agency revealed today. The news comes weeks after the CDC announced that dozens of its employees were potentially exposed to anthrax because its staff did not follow established laboratory safety guidelines.

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In response to the incidents, the CDC today imposed a moratorium on shipments from its high-biosecurity facilities and shut down the laboratories responsible for the anthrax and H5N1 incidents, pending an investigation. “I'm disappointed by what happened and frankly I'm angry,” agency director Thomas Frieden said at a press conference.

After news of the anthrax exposure broke on 19 June, the CDC began investigating why its lab workers did not follow proper procedure to inactivate Bacillus anthracis spores before shipping them to another lab on the agency’s Atlanta campus. The receiving lab was not equipped to handle the pathogen, and once the mistake was discovered, more than 70 people were pre-emptively treated for anthrax infection. The CDC now says that the lab never needed to work with B. anthracis in the first place; another bacterium would have sufficed to test the diagnostic equipment that the lab was evaluating. The good news, Frieden says, is that the CDC now does not believe that anyone was actually exposed to anthrax spores.

But the agency’s ongoing investigation has revealed more bad news: on 12–13 March, the CDC’s influenza lab contaminated a harmless flu strain with the highly dangerous H5N1 variety, and sent it to a laboratory operated by the US Department of Agriculture (USDA) in Athens, Georgia. The mistake was discovered on 23 May, but Frieden says that he was not notified until 9 July. “Why it took six weeks for that to be made apparent, I can think of no valid explanation,” he says. The USDA lab was equipped to handle highly infectious agents, and the agency is confident that there were no exposures.

Risky business

According to a CDC report released on 11 July, at least five such incidents have happened in the past decade, in which CDC shipments of potentially viable pathogens — including those that cause botulism, anthrax and brucellosis — were improperly inactivated or wrongly believed to be harmless. “These are wakeup calls,” Frieden says. “These are events that tell us we have a problem, and we are going to fix it.”

The CDC says that it will work with an external scientific advisory panel to examine safety procedures at all of its high-level biosafety labs before resuming any shipments to internal or external labs. The influenza and anthrax labs are shut indefinitely, pending completion of the investigations, but Frieden expects that the influenza lab will reopen in time for tracking the flu season this autumn.

The agency is also instituting new safety measures, including a review of its training procedures and appointing CDC health-care safety expert Michael Bell to act as a single point of accountability for future biosafety incidents. Frieden also says that employees who are found to have knowingly violated lab safety procedures will face disciplinary action.

News of the CDC troubles “points out that accidents can happen anywhere”, even at the agency charged with overseeing US biosecurity, says Michael Osterholm, a public-health expert at the University of Minnesota in Minneapolis. He sees the H5N1 incident as a reason to question 'gain-of-function' research that involves engineering disease-causing viruses to make them more deadly, in order to understand what might happen if such viruses evolved naturally to become more pathogenic.

If there is any silver lining to the CDC incidents, Osterholm says, “it’s that we will have a heightened level of lab safety and a discussion that I think has been long overdue.”

The CDC’s actions come on the heels of another biosafety scare earlier this week, when unauthorized vials of smallpox were found in a cold storage room on the National Institutes of Health campus in Bethesda, Maryland. The CDC said today that its tests show that virus samples from at least two of the twelve vials were able to successfully infect and replicate in cultured human cells. Frieden says that the vials will now be destroyed with the World Health Organization in attendance as a witness. “That’s what should have been done a couple decades ago,” he says.