The U.S. Centers for Disease Control and Prevention is advising some employees to stop taking antibiotics to ward off a possible anthrax infection after preliminary tests suggest it is "highly unlikely" they were inadvertently exposed to live anthrax bacteria earlier this month, a spokesman said on Monday.
The CDC conducted the tests after an incident in the agency's high-security bioterror response laboratory suggested live anthrax may have been transferred from that lab to employees in a lower-security facility who were not wearing proper protective gear, raising concerns that they may have been exposed to the deadly pathogen.
CDC spokesman Tom Skinner said preliminary results of environmental testing in the lower-security labs and some lab tests by the CDC suggest no viable bacteria left the lab.
Based on those results, most of the employees involved have been determined "to have no increased risk of exposure."
In addition to the testing, the CDC gave the employees a questionnaire asking how close they had come to the areas where the anthrax was worked on. Two groups of staff were selected: One including staff potentially exposed to aerosols in affected laboratory space and a second group not potentially exposed but having worked in or near affected laboratory space.
"Employees in these groups are having one-on-one appointments with medical staff in CDC's occupational health clinic who are reviewing all information with them and discussing the pros and cons of continuing post-exposure prophylaxis as part of shared decision making," Skinner said.
Some 29 individuals in the first group are being advised to continue taking antibiotics; 33 individuals in the latter group are being advised to stop taking them.
The CDC said a third group of employees who were initially thought to have been exposed were determined not to require treatment.
Dr. Harold Jaffe, the CDC's associate director for science, is leading an internal investigation into the circumstances surrounding this incident. He will submit a report to CDC Director Dr. Tom Frieden in early July.
In addition, the U.S. Department of Agriculture is conducting an independent investigation.
Based on final results of these investigations, CDC said it will take appropriate action in the individual laboratory, as well as any actions indicated for all laboratories which work with dangerous microbes at CDC, and will consider broader implications for laboratory safety.
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