CDC Report Documents Ninth Known Case of Welder’s Anthrax
A welding apprentice in Louisiana with welder’s anthrax, a form of severe pneumonia caused by Bacillus cereus group bacteria that produce anthrax toxin, was successfully treated with the antitoxin obiltoxaximab, according to a CDC report published on Jan. 1. The agency’s Morbidity and Mortality Weekly Report (MMWR) explains that the patient was hospitalized in September 2024 with pneumonia and respiratory failure and required intubation and mechanical ventilation. His case of welder’s anthrax is only the ninth to be documented since CDC first identified the disease in 1994.
The worker was diagnosed at 18 years old, making him the youngest worker to be diagnosed with the disease. The previous cases affected welders or metalworkers from Louisiana and Texas in their 30s, 40s, or 50s, and six were fatal.
CDC’s new report describes the 18-year-old worker’s medical treatment as well as the subsequent investigation of his work site that sought to identify the environmental source of his infection. The investigation was performed by the Louisiana Department of Public Health (LDH) with assistance from CDC and NIOSH. LDH’s interviews of the patient and representatives from his workplace explored his exposure history and welding practices at the site where the patient worked in the shipbuilding and repair industry.
“He conducted shielded metal arc welding using carbon steel and low-hydrogen carbon steel electrodes both in open areas and confined spaces with limited ventilation and minimal use of personal protective equipment,” the CDC report explains. “No fans or ventilation systems were present in the patient’s work area, including within enclosed spaces.”
Interviews conducted as part of the investigation also showed that workers at the site did not consistently wear respiratory protection when welding and would often eat in their work area even though a designated break area was available.
Investigators took a variety of samples from the site, including bulk soil samples from work areas, samples from tools or items the patient may have used, and samples from outdoor areas, buildings, and break areas near where he worked. Twenty-eight of the 245 total samples collected were positive by quantitative real-time polymerase chain reaction for anthrax toxin genes. The positive samples included one swab sample from work gloves and two sponge samples from a handrail and a table in an area where the patient worked, plus 25 soil samples from across the site.
The report’s authors were not able to definitively conclude why the patient was the only worker to become ill when anthrax toxin genes were detected in multiple samples from around the site. The report notes that the patient “had a relatively brief history of working as a welder” and did not have comorbidities and risk factors like several of the patients with previous cases of welder’s anthrax.
“However, shielded metal arc welding produces more fumes than other types of welding do, which might facilitate respiratory infection via immune system suppression,” the authors suggest. “Positioning, skill level, use of exhaust ventilation systems, and time spent welding could also contribute to the duration and intensity of welding fume exposures among welders.”
CDC’s report recommends engineering control such as wet sweeping and high efficiency particulate air filter vacuuming methods to clean welding surfaces and other workspaces to help reduce workers’ exposure to soil that could be contaminated with B. cereus bacteria. The agency also recommends the use of ventilation systems in enclosed areas. PPE that reduces workers’ exposure to metal fumes and dust may also reduce their risk for welder’s anthrax, the report adds.
The full report is available online in CDC’s MMWR.