Abstract Bacillus cereus group bacteria containing the anthrax toxin genes can cause fatal anthrax pneumonia in welders. Two welder's anthrax cases identified in 2020 were investigated to determine the source of each patient's exposure. Environmental sampling was performed at locations where each patient had recent exposure to soil and dust. Samples were tested for the anthrax toxin genes by real-time PCR, and culture was performed on positive samples to identify whether any environmental isolates matched the patient's clinical isolate. A total of 185 environmental samples were collected in investigation A for patient A and 108 samples in investigation B for patient B. All samples from investigation B were real-time PCR-negative, but 14 (8%) samples from investigation A were positive, including 10 from patient A's worksite and 4 from his work-related clothing and gear. An isolate genetically matching the one recovered from patient A was successfully cultured from a worksite soil sample. All welder's anthrax cases should be investigated to determine the source of exposure, which may be linked to their worksite. Welding and metalworking employers should consider conducting a workplace hazard assessment and implementing controls to reduce the risk of occupationally associated illnesses including welder's anthrax.

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.†