Researchers unknowingly used real anthrax in tests

No infections, but a cautionary tale

Like an electrician unknowingly working with hot wires, researchers at a hospital in California found that a benign biological surrogate they were working with actually contained anthrax spores. Consider this cautionary tale from the Centers for Disease Control and Prevention (CDC).1

On June 9, 2004, the California Department of Health Services (CDHS) was notified of possible inadvertent exposure to Bacillus anthracis spores at Children’s Hospital Oakland Research Institute (CHORI), where workers were evaluating the immune response of mice to B. anthracis.

Hospital researchers had injected 10 mice with a suspension believed to contain nonviable vegetative cells of B. anthracis Ames strain. The suspension was centrifuged and drawn into syringes on an open bench in the laboratory. The mice were injected in a separate animal-handling facility at CHORI. By May 30, all of the injected animals had unexpectedly died. The carcasses were removed from the cages, placed into a plastic biohazard bag, and frozen. The bedding was discarded as standard animal waste. The cages were sanitized in an automated washer.

A sample of the original suspension was cultured and grew nonhemolytic gram-positive rods consistent with B. anthracis. Because staff believed they were working with inactive organisms, they had performed these activities on an open bench, and appropriate personal protective equipment (PPE) was not used consistently until after the deaths of a second group of mice.

Twelve people were involved in either the lab or its animal-handling facilities. Three had direct contact with the bacterial suspensions, cultures, or infected animals. Although at low risk for inhalation of B. anthracis spores, to further reduce their risk, the three workers with direct contact were recommended for post-exposure chemoprophylaxis for prevention of inhalational anthrax (i.e., either ciprofloxacin 500 mg or doxycycline 100 mg, orally twice daily for 60 days). The nine people who worked in the lab or animal-handling facility but who did not have direct contact were offered the same chemoprophylaxis regimen. Eight of the 12 potentially exposed people opted to take chemoprophylaxis, including the three for whom the regimen was recommended. None of the potentially exposed people had symptoms consistent with anthrax.

"The findings in this investigation indicate that workers in a research laboratory unknowingly received and used a suspension from a contract laboratory that likely contained viable B. anthracis organisms," the CDC concluded. ". . . CDC continues to work with state agencies and other federal agencies to investigate processing procedures at the contractor facility to determine why the suspension contained viable B. anthracis organisms."

One theory is that the heat-killing procedures used by the contractor might have been lethal to vegetative cells, but anthrax spores survived. Regardless, inactivated suspensions of B. anthracis should be cultured both at the preparing lab before shipment and at the research lab several days before use to ensure sterility, the CDC added. Such procedures would increase the probability of detecting even a small number of viable B. anthracis spores. CHORI staff did not perform sterility testing on the suspension received in March 2004.

Because inhalation of viable B. anthracis spores can result in fatal infection, the CDC recommends lab personnel who routinely perform activities with clinical materials and diagnostic quantities of infectious cultures implement biosafety Level 2 (BSL-2) practices. These practices include use of appropriate PPE (e.g., gloves, gowns, or lab coats) and a safety cabinet for procedures with the potential to expel infectious aerosols (e.g., centrifuging or ejection of pipette tips). Face protection (e.g., goggles, faceshield, or splatter guard) should be used against anticipated splashes or sprays when potentially infectious materials require handling outside of the cabinet.

"Research laboratory workers should assume that all inactivated B. anthracis suspension materials are infectious until inactivation is adequately confirmed," the CDC stressed.


1. Centers for Disease Control and Prevention. Inadvertent laboratory exposure to Bacillus anthracis — California, 2004. MMWR 2005; 54(12):301-304.