The worker handled the spores a day after he had cut his jaw while shaving, the Centers for Disease Control and Prevention reported. He then apparently touched his face and developed an anthrax sore on his jaw.
The man was put on antibiotics and is recovering.
It was the first known anthrax case in the United States since the anthrax-by-mail attacks that killed five people and sickened 13 more.
None of the 40 workers at the lab had been vaccinated against anthrax, the CDC said.
The CDC has not identified the worker or the lab.
The infection apparently happened March 1 as the worker was moving vials from a cabinet into a freezer, the CDC said. He was not wearing gloves, contrary to federal health recommendations, the agency said.
Over the next few days, the shaving cut became larger and the man reported swelling on his neck and a low-grade fever. He spent five days in the hospital and is expected to make a full recovery.
"The most likely thing would be that the spores were on his hand and when he touched the open wound he transferred them," said Dr. Elena Page, a CDC occupational safety expert.
The CDC also noted that the laboratory where the man worked had not used a recommended 10-percent bleach solution to kill potential anthrax spores on storage vials because the bleach caused labels to dislodge.
The CDC said the case highlights the need for workers who regularly handle anthrax specimens to be vaccinated against the disease. Workers at many anthrax labs already are.
The private laboratory was one of several the CDC contracted with to work through a backlog of samples collected during the peak of the anthrax attacks.
The infected man has been treated with antibiotics and is expected to make a full recovery.
None of his co-workers have fallen ill and all environmental samples from the laboratory, with the exception of one taken from the top of the suspected storage vials, have tested negative for anthrax, the CDC said.
Five people died and 13 others became infected with anthrax in 2001 during an outbreak linked to mail delivered in the weeks following the Sept. 11 attacks on the United States.
The last case, that of a 94-year-old Connecticut woman, was reported on Nov. 20. The woman died of inhalational anthrax, the most serious form of the disease, the next day.
The CDC, which was in the forefront of the battle to respond to the outbreak, has contracted with a number of private laboratories to process a backlog of specimens collected during the height of the scare.
The CDC has listed the Texas case as suspected anthrax because a swab of the man's lesion had been processed in his own laboratory, raising the possibility that it might have occurred due to cross-contamination.
It noted, however, that the man's symptoms and environmental exposure were consistent with skin anthrax.