Welder's Anthrax in an 18-Year-Old Louisiana Apprentice, 2024, Treated With Antitoxin

Welder's anthrax is a recently described, life-threatening pneumonia caused by Bacillus cereus group bacteria that make anthrax toxin. Before 2024, eight cases had been reported, all in welders or metalworkers from Louisiana or Texas — and six were fatal.

CDC's visual summary of the report.

Anthrax and its relatives

Anthrax is caused by Bacillus anthracis, one of the B. cereus group — closely related, spore-forming bacteria that also include B. cereus and newly recognized species such as B. tropicus. B. anthracis carries its toxin and a protective capsule on two plasmids (pXO1 and pXO2). Depending on how spores enter the body, anthrax can be cutaneous, gastrointestinal or inhalation anthrax; inhalation anthrax kills about 55% of patients even with prompt, aggressive treatment, and nearly all untreated patients.

B. cereus usually causes food poisoning, but some B. cereus group strains, including B. tropicus, carry a version of pXO1 with an anthrax toxin gene. Since 1994, seven cases of severe pneumonia have been found in immunocompetent metalworkers — mostly welders — infected with such strains; an eighth, from 1996, was later identified by sequencing archived isolates. These strains may live in soil, sediment, dust or vegetation in the southern United States.

The ninth case

• September 7, 2024: a clinician contacted CDC and the Louisiana Department of Health about a previously healthy 18-year-old man admitted to intensive care with severe pneumonia and respiratory failure, on a ventilator. His cough had begun a week earlier.
• He had worked part-time as a welder for the 6 months before; no smoking, vaping or heavy drinking.
• Blood cultures grew B. cereus group bacteria; with his pneumonia, job and the location of earlier cases, welder's anthrax was suspected.

Treatment

• First, vancomycin, meropenem, ciprofloxacin and doxycycline.
• CDC obtained obiltoxaximab (Anthim) — a monoclonal antibody antitoxin against the anthrax toxin's protective antigen, approved for inhalation anthrax — from the U.S. Strategic National Stockpile. He received it 34 hours after welder's anthrax was suspected, about a week after his symptoms began.
• He improved rapidly: he came off the ventilator 72 hours later. He also had continued intravenous antibiotics and drainage of a pleural effusion.
• Discharged after 26 days on a tailored antibiotic course; by his 3-month follow-up, all his lung symptoms had resolved.

Laboratory: Louisiana's public health laboratory confirmed an anthrax toxin gene by PCR; CDC identified the bacterium as Bacillus tropicus, sequence type ST-78, carrying B. anthracis–associated toxin genes.

His work

He worked 4 hours a day, 4 days a week as a welding apprentice in shipbuilding and repair, doing shielded metal arc welding with carbon steel and low-hydrogen carbon steel electrodes — in open areas and in confined spaces with limited ventilation, no fans or ventilation systems, and little protective equipment. Workers there did not always wear respirators, and often ate lunch in the work area instead of the break area.

The worksite

Investigators collected 245 samples — 95 of soil, 98 sponge-stick and 52 swab samples from tools and surfaces he may have used, and more from outdoor areas, clothing, buildings and break areas.

One soil sample yielded a culture — ST-78, like him; all other known ST-78 strains are B. tropicus. Its genome was 99.998% identical to his, and both clustered with isolates from earlier Louisiana patients, a Louisiana zoo animal, the Louisiana environment, and patients from Florida and Texas.

Genetic relatedness of B. tropicus isolates from patients with welder's anthrax, a zoo animal and the environment, United States, 1994–2025. CDC.

All nine cases

All but case 5 were men.

What it means

Fast recognition and a coordinated response likely helped him recover and survive. Only three of the nine patients have survived — two of them after antitoxin; none of the six who died received it. This was the first clinical use of obiltoxaximab for an anthrax-like illness.

• Where: B. cereus group bacteria are everywhere, but welder's anthrax has been documented only in Texas and Louisiana, and toxin-carrying strains found in the environment only in Louisiana. Modeling suggests conditions suit them in many states, including Arkansas, Louisiana, Mississippi, Oklahoma and Texas.
• Why welders: welding fumes harm the lungs and weaken their immune defenses; shielded metal arc welding makes more fume than other methods. Half of the earlier patients had other risk factors; this one had none and a short welding career, and why he alone fell ill is unclear.
• Prevention at work (CDC and Louisiana's advice to the site): a labor-management safety committee and a hazard assessment program; keep work surfaces free of dust and dirt; clean by wet sweeping and high-efficiency particulate air filter vacuuming; ventilate enclosed spaces; teach workers about the disease; eat and store food only in break areas; and provide protective equipment and NIOSH-approved respirators with medical clearance, fit testing and training. How far these were adopted is not known.

For clinicians

• Consider welder's anthrax in welders and metalworkers with pneumonia, especially in the southern United States.
• Follow the guidelines for inhalation anthrax — multidrug therapy with bactericidal drugs and protein synthesis inhibitors (e.g., ciprofloxacin and clindamycin); B. cereus group bacteria are often resistant to penicillins and cephalosporins.
• Tell the health department and consult CDC as soon as it is suspected, to get antitoxins such as obiltoxaximab from the Strategic National Stockpile.
• Anthrax vaccination has not been studied in welders.

Limitations: his clothing, gloves and boots were not kept, so the items he used could not be tested, and his exposure history rests on interviews and a look at the site after his illness.

Sources

Based on Thompson JM, Lundstrom EW, Hein LD, et al., "Welder's Anthrax Treated with Obiltoxaximab — Louisiana, 2024," MMWR Morbidity and Mortality Weekly Report, volume 74, Centers for Disease Control and Prevention; a work of the United States government in the public domain.