A few dozen U.S. troops will have exposure to laboratory samples from potential Ebola patients by running testing facilities in Liberia, the head of U.S. Africa Command said.

While most of the 4,000 troops authorized to deploy to the west African country won’t have direct exposure to the virus — as Pentagon officials have previously emphasized — three or four specially trained personnel will run each of as many as seven testing labs, Army General David Rodriguez said today at a Pentagon news conference.

“They are specifically trained to do that,” Rodriguez said of the lab personnel, which he called a “specialty element” of the larger force.

In a statement after the news conference, Rodriguez said he had erroneously indicated that the military personnel would have direct contact with potential Ebola patients. In fact, he said, lab personnel will test “only samples.”

“The testing labs are manned by highly skilled and trained personnel from the U.S. Naval Medical Research Center,” Rodriguez said. “These labs provide 24-hour turnaround results on samples received from area clinics and health-care providers, with the capability to process up to 100 samples per day.”

Lab personnel will wear full protective gear, he said at the briefing.

Three labs already have been set up in the country to respond to the epidemic and the military has received a request for four more, Rodriguez said.

Most of the troops in Liberia will focus on logistics, training and engineering support and won’t have direct contact with potential Ebola victims, he said. Troops are helping to build treatment centers.

The U.S. mission in Liberia, which may last for about a year, is likely to cost about $750 million for the next six months, he said.