Bacillus anthrax vegetative cells and spores. Last month, dozens of scientists were exposed to the dangerous pathogen. A second investigation by the USDA found more lapses in safety protocol than the CDC’s internal review of the incident. (U.S. Department of Defense/AFP/Getty Images)

A second U.S. investigation into last month’s mishandling of anthrax bacteria at federal government laboratories in Atlanta has found additional safety lapses, such as anthrax stored in unlocked refrigerators in unrestricted hallways, according to a document released Monday by a House committee.

The findings by investigators from a special unit of the Agriculture Department raise additional concerns about the scope of the incident and the culture of laboratory safety at the Centers for Disease Control and Prevention, where the incident took place. They also add troubling new context to last month’s anthrax scare, in which as many 84 workers were exposed to live anthrax after employees unknowingly sent samples of the bacteria from one CDC lab to some of its other ones.

A House Energy and Commerce subcommittee has scheduled a hearing Wednesday on the anthrax incident. But CDC Director Thomas Frieden, who is scheduled to testify, is certain to be questioned about numerous other incidents over the past decade in which the CDC has said it mishandled deadly microbes. In addition to the recent anthrax lapse, for example, agency researchers this year mistakenly sent a virulent strain of bird-flu virus to a USDA lab in Georgia.

“Each layer we peel back in this investigation seems to reveal a new instance of carelessness in the CDC’s management of dangerous pathogens,” Rep. Tim Murphy (R-Pa.), who heads the oversight subcommittee, said in a statement.

After the June anthrax incident, the CDC conducted an internal investigation and asked the USDA’s Animal and Plant Health Inspection Service (APHIS) to conduct a parallel probe. The USDA’s findings outline a litany of mishaps, according to a background memo prepared by the congressional subcommittee:

●There were missing anthrax containers that had to be tracked down by USDA inspectors.

●Dangerous materials were transferred using Ziploc bags, which do not meet the “durable” requirement for secondary containment.

●Anthrax was stored in unlocked refrigerators in an unrestricted hallway, and workers freely passed through the area at the time of inspection; the key to one of the refrigerator doors sat in its lock.

●Some lab workers who potentially were exposed were not examined for five days following notification.

●Disinfectant used to decontaminate vials and bags had expired, and researchers could not remember whether they had used expired bleach to decontaminate areas after the potential release was identified.

The USDA submitted its report to the CDC last week, a day before the CDC released its accounting of security lapses over the past decade.

“We are carefully scrutinizing their report,” CDC spokesman Tom Skinner said. The CDC has already implemented some of the recommendations, and “we’re moving to address others as quickly as possible.”

Legislation in 2002 required the Department of Health and Human Services to regulate certain highly toxic pathogens that have the potential to pose severe public health threats, such as smallpox and anthrax. Within the agency, that task falls to a division within the CDC. In addition, the USDA’s APHIS oversees toxins that could pose serious threats to animal or plant health. Sometimes the toxins on those lists overlap.