In 2020, CDC confirmed two cases of pneumonia (one fatal) in welders caused by rare Bacillus cereus group bacteria containing anthrax toxin genes typically associated with Bacillus anthracis. B. cereus group bacteria are gram-positive facultative anaerobes, often toxin-producing, that are ubiquitous in the environment and reside naturally in soil and dust (1). B. cereus can also be found in food, and although infection typically causes illnesses characterized by diarrhea or vomiting, B. cereus can have other clinical manifestations (e.g., pulmonary, ocular, or cutaneous). Among seven persons in the United States reported to be infected with B. cereus group bacteria containing anthrax toxin genes resulting in pneumonia since 1994, five patients died and two had critical illness with prolonged hospitalization and recovery (2–5). All persons with pneumonia were welders or other metalworkers who had worked in Louisiana or Texas (Table). In addition to the seven pneumonia cases, a cutaneous infection with B. cereus group bacteria containing anthrax toxin genes has been reported in a patient with an anthrax eschar in Florida.^†

Understanding the extent to which Bacillus species other than B. anthracis carry anthrax toxin genes and whether their geographic range extends beyond the U.S. Gulf Coast states is limited. Furthermore, little is known about why these highly fatal pneumonia cases have only been detected among welders and other metalworkers. Long-term exposure to welding and metalworking fumes is associated with various forms of lung injury that can cause changes in lung function and increase susceptibility to pulmonary infections, including fatal pneumonia.^§ An investigation by CDC at one patient’s worksite in Louisiana (patient F) identified a bacterial isolate in a soil sample that genetically matched a clinical isolate from the patient. However, it is unclear why only one person at each worksite became ill and what environmental or host risk factors might have facilitated the exposure and infection.

Several actions can decrease risk for lung injury or infection, including anthrax pneumonia caused by B. cereus group bacteria, among welders and other metalworkers. Because of the association between welding or metalworking and pulmonary infections or injury, it is important that employers educate workers regarding hazards associated with welding and measures they can take to minimize potential exposures. Welding and metalworking employers, trade associations, and unions might consider targeted outreach to increase workers’ awareness about pulmonary infections, including anthrax, especially those workers in the U.S. Gulf Coast states. In addition, employers should conduct a hazard assessment at worksites and consider the use of National Institute for Occupational Safety and Health–approved respirators as part of a written respiratory protection program.^¶,**

Clinicians should consider B. cereus group bacteria in the differential diagnosis when treating welders and other metalworkers with severe, rapidly progressive pneumonia or other anthrax-like disease.^†† B. cereus group bacteria identified on culture are not always contaminants; when B. cereus with anthrax toxin is suspected, laboratorians and clinicians should pursue additional testing through their state Laboratory Response Network laboratory.^§§ Regional health departments and the Laboratory Response Network serve pivotal roles in pathogen detection and procuring anthrax antitoxin for confirmed cases.