In the past 20 years, there have been only nine anthrax cases in the US.

However, B. anthracis is part of the larger Bacillus cereus group, which also includes B. cereus and B. tropicus, a newly recognized species. And these species can also carry and produce anthrax toxins. Both can be found in soils, and B. cereus is considered ubiquitous in the environment.

In 2022, CDC researchers found an unexpected pattern. Since 1997, there had been seven cases of infections from Bacillus group bacteria producing the anthrax toxin—all in metalworkers. Six of the seven were welders, hence the term “welder’s anthrax,” with the remaining case in a person working in a foundry grinding metal. Of the six cases where a specific Bacillus species was identified, B. tropicus was the culprit, including in the newly reported case.

Speculating risks
It’s unclear why metalworkers, and welders specifically, are uniquely vulnerable to this infection. In their 2022 report making the connection, CDC experts speculated that it may be a combination of having weakened immune responses in the lungs after inhaling toxic metal fumes and gases created during metalwork, and having increased exposure to the deadly germs in their workplaces. //

Environmental sampling of his workplace found anthrax-toxin-producing Bacillus in 28 of 254 spot samples. //

The experts also speculated that iron exposure could play a role. Bacillus bacteria need iron to live and thrive, and metalworkers can build up excess iron levels in their respiratory system during their work. Iron overload could create the perfect environment for bacterial infection. In the teen’s case, he was working with carbon steel and low-hydrogen carbon steel electrodes.

For now, the precise risk factors and why the healthy teen—and not anyone else in his workplace—fell ill remain unknown. CDC and state officials recommended changes to the workplace to protect metalworkers’ health, including better use of respirators, ventilation, and dust control.