Officials say there are no signs anyone got sick from anthrax after a lab safety problem at the US Centres for Disease Control and Prevention.
Earlier this month, the CDC said dozens of workers at three labs in Atlanta may have been accidentally exposed to anthrax.
But on Monday, CDC officials said anthrax spores have not been found on surfaces in the labs and it's not clear that any dangerous anthrax was released.
About 60 workers were offered antibiotics and vaccinations as precautionary treatment. The CDC says about half can now stop taking the medication.
A CDC internal report on what went wrong is expected later this week. Earlier, the federal agency said anthrax samples used in research hadn't been sterilised as expected.
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