A scientist separates blood cells from plasma cells to isolate any Ebola RNA to test for the virus at a European mobile laboratory in Gueckedou, Guinea. (Reuters)

U.S. officials are scrambling to resolve a key logistical hurdle in fighting the fast-moving Ebola epidemic in Liberia: the ability to transport blood samples from remote areas of the country for laboratory testing.

In recent weeks, the outbreak in Liberia has changed. Aid workers are responding to Ebola “brush fires” that pop up daily, often in hard-to-reach spots. Teams often travel hours, even days, on foot or in canoes to reach suspected Ebola patients in villages and towns.

Once they collect blood samples, however, there have been delays in getting the specimens transported by helicopter to labs for testing, aid groups say. In one recent case, a helicopter operated by a United Nations crew refused to take the samples. Workers had to transport them by ground, delaying testing by two days, said Ken Isaacs, a vice president of the Christian relief group Samaritan’s Purse.

The U.S. military has helicopters in Liberia, but its mission “does not include direct contact with patients, handling of patients, or of the blood samples,” Pentagon spokesman John Kirby said Thursday.

A key to controlling the spread of the virus is reducing the time that sick people are left undiagnosed and potentially contagious.

“There needs to be stronger coordination,” Isaacs said. “It’s very frustrating.”

The logistics challenges come at a time when some parts of Liberia are seeing a marked decline in new cases but neighboring Sierra Leone is experiencing a surge. In a conference call with reporters Thursday, Thomas Frieden, director of the Centers for Disease Control and Prevention, said the CDC no longer is forecasting exponential increases in Sierra Leone and Liberia, but the number of cases across the region is still “stunningly large.”

Congress is weighing the Obama administration’s request for more than $6 billion in additional resources to fight the epidemic in West Africa and shore up U.S. preparedness.

Some emergency funds could be used to accelerate research for a rapid diagnostic test that aid workers could carry in their pocket to remote locations, Frieden said.

“The whole issue with specimen and transport are being worked through in real time,” said Jeremy Konyndyk, a top official at the U.S. Agency for International Development, who also was on the conference call. USAID is working on a civilian solution for helicopters, he said, and a decision is likely next week.

During the earlier months of the epidemic this spring, Samaritan’s Purse used its helicopters to pick up blood samples from different charities and government agencies. All groups followed the same protocol for packaging and getting specimens on and off planes, Isaacs said. Pilots never touched the specimen packages.