Alison Young

USA TODAY

The Centers for Disease Control and Prevention is investigating how one of its own lab workers became infected with a strain of salmonella that was being used as part of their job, the agency announced Thursday.

The possible lab-acquired infection is the latest in a series of incidents at the Atlanta-based agency, including previous mishandling of specimens of anthrax, Ebola and a deadly strain of avian influenza.

The CDC said the lab worker who was sickened with salmonella had been infected with a strain that has a relatively rare DNA fingerprint. Salmonella, which is usually spread through contaminated food, typically causes diarrhea, fever and abdominal cramps that can last from four to seven days.

"The worker is well and back at CDC and, based on what we know now, no other staff were exposed or sick, and there was no release outside the laboratory," the agency said in a press release.

The worker had completed all required safety training and was following standard protocols while performing a procedure on a frozen sample of salmonella in an effort to grow the bacteria, the CDC said. In the days following the procedure, the worker became ill and on March 18 informed the agency they had been diagnosed with a salmonella infection. The agency said it is investigating to see if additional laboratory safeguards are needed to prevent exposures in the future.

Biosafety experts expressed concern about the infection, but praised the CDC for identifying it and notifying the public.

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"I think the important thing here is that the CDC learned from its past mistakes and is now practicing transparency," said Scott Becker, executive director of the Association of Public Health Laboratories. Becker, who noted that lab work carries risks, said the CDC's new lab safety office will play an important role in reviewing the policies and procedures to determine what happened in the incident.

Sean Kaufman, a biosafety consultant who has testified before Congress, said it's good news that mechanisms were in place to identify when a lab worker got sick. But Kaufman said he remains concerned that CDC has not addressed systemic issues with lab safety.

"Even though CDC has taken steps in the right direction, there continues to be a stream of incidents and accidents," Kaufman said.

Exactly how many lab incidents have occurred at CDC in recent years is unclear because the agency has been slow to release records under the federal Freedom of Information Act. Last year, the CDC told the USA TODAY NETWORK it will take until sometime in 2018 before it will release reports of all incidents that occurred at the agency's labs in Atlanta and Fort Collins, Colo., during 2013 and 2014.

A summary of lab incidents the agency provided to the news organization was incomplete and revealed the CDC lacked a key policy to ensure top agency safety officials received reports of mishaps, despite promises to Congress of reforms.

The USA TODAY NETWORK's "Biolabs in Your Backyard" investigation, published throughout 2015, revealed that incidents at the CDC are among hundreds that have occurred corporate, university, government and military labs nationwide. It also exposed a system of fragmented federal oversight and pervasive secrecy that obscures failings by facilities and regulators. The series has been cited in ongoing congressional investigations and in new transparency reforms called for by White House science and homeland security advisers. In November, the CDC replaced the head of its laboratory regulation program, which inspects biodefense labs nationwide that work with potential bioterror pathogens.

Top U.S. lab regulator replaced in wake of incidents with bioterror pathogens

The CDC's high-profile 2014 incidents involved potential bioterror pathogens like anthrax and Ebola occurred in biosafety level 3 and 4 labs — the two highest safety levels — where scientists wear specialized gear ranging from respirators to full-body, spacesuit-like protection. The new salmonella incident involved a common strain of the bacterium that causes food-borne illnesses and it occurred at a biosafety level 2 lab where workers may only wear gloves, gowns and face masks.

Kaufman said it's important to have a strong culture of safety and attention to detail in all levels of labs to ensure workers don't get sick and potentially spread illness to their families. "There was some sort of breakdown in those procedures and someone got sick," he said of the latest incident.

Read the USA TODAY NETWORK's "Biolabs in Your Backyard" investigation at biolabs.usatoday.com.

Follow investigative reporter Alison Young on Twitter: @alisonannyoung