April 28, 2022

Researchers Describe Welder’s Anthrax, a Newly Identified Occupational Disease

An article recently published in the journal Pathogens highlights cases of “welder’s anthrax,” or severe pneumonia in a metalworker caused by Bacillus cereus group bacteria that produce anthrax toxin. The authors of the paper characterize welder’s anthrax as “a newly identified, deadly occupational disease.” According to the journal article, seven cases of welder’s anthrax were reported to CDC during 1994–2020. Six of the patients had the job title “welder,” and the seventh patient was a metalworker. Two additional welders were reported to have “rapidly progressive fatal pneumonia” in 1996 and 1997, but these cases do not meet the new case definition of welder’s anthrax because the patients’ infections were caused by B. cereus that were found not to have anthrax toxin genes. Although welder’s anthrax is rare, researchers believe that cases may have been missed due to several factors, including limited detection and understanding of this pathogen.

A CDC report published in October describes B. cereus group bacteria as “gram-positive facultative anaerobes, often toxin-producing, that are ubiquitous in the environment and reside naturally in soil and dust.” The Pathogens journal article discusses possible mechanisms of infection and disease, including the hypothesis that the risk of infection is primarily from occupational exposure to metal fumes. The authors note that previous research findings suggest that inhalation of metal fumes may predispose workers to lung infections.

“The mechanisms associated with the immunosuppressive effects of metal fumes after inhalation are mostly unknown,” the authors explain, but “[t]heories have included that metal fumes (or iron) act as a growth nutrient for bacteria, enhance the binding of bacteria to lung tissues, or impair immune responses in the lung through oxidative stress.”

B. cereus anthrax toxins need iron to survive, and earlier studies have found that soil iron is much higher around welding sites than elsewhere. The authors of the recent article state that it’s unclear whether occupational activities also contribute to increased exposure to pathogens such as B. cereus but note that the infecting strain of one of the welders was found in a soil sample taken from his work site.

Researchers urge communication and cooperation between clinicians, employers, and public health practitioners to identify cases of welder’s anthrax and identify occupational and personal risk factors. They also recommend future research to examine the possibility of increased susceptibility to and severity of lung infection among welders and metalworkers. The authors also call for additional research to study the effectiveness of interventions such as engineering controls and respiratory protection in minimizing workers’ exposures to metal fumes as well as research that seeks to better understand the interplay between exposure to metal fumes and other welding hazards.

The article in Pathogens was authored by researchers from NIOSH and CDC’s Bacterial Special Pathogens Branch. The full text of the article is available to read on the website of the publisher MDPI.