An anthrax scare in July this year was the latest in a string of security lapses at the US Centers for Disease Control and Prevention (CDC), the federal agency charged with preventing the spread of infectious diseases. Roughly 84 workers at CDC’s Atlanta headquarters may have been exposed to the deadly bacterium, Bacillus anthracis, after a breach at the agency’s Bioterrorism Rapid Response and Advanced Technology Laboratory, the agency said. The number of workers being monitored for anthrax was revised from 75 when the lab breach was announced.

At least three different incidents between 2007 and 2012 also called into question the CDC’s laboratory security system, which is designed to keep dangerous pathogens like smallpox, monkey pox and SARS from escaping into the general population. No illnesses were reported in connection with the incidents, all three of which involved malfunctioning airflow and ventilation systems.

The possession, use and transfer of dangerous biological select agents and toxins, including Bacillus anthracis, are overseen by the Federal Select Agent Program, which is operated by CDC in conjunction with agents from the US Department of Agriculture.

The 84 workers involved in the anthrax scare have been offered antibiotics and vaccination, CDC officials said, adding that at least 54 of the workers have been examined and 27 have been vaccinated. So far, none have shown signs of illness, but symptoms can take two months to appear, according to the agency. Left untreated, the inhaled form of anthrax can be deadly in 85 per cent of cases, according to the CDC. Even with treatment, the fatality rate is as high as 45 per cent. Anthrax is not contagious and the general public is not at risk, CDC officials said.