Health officials at Landstuhl Regional Medical Center in Germany are still awaiting test results of four servicemembers believed to have the virus H1N1, or swine flu.

Due to restrictions on shipping lab specimens over the weekend, results won’t be in hand for another 24 to 48 hours, Europe Regional Medical Command spokesman Steve Davis said Monday afternoon.

Two Germany-based soldiers at Landstuhl were confirmed positive for swine flu last week — the first known cases of H1N1 among U.S. military personnel in Europe.

The four servicemembers with pending test results are "probable" cases, Landstuhl health officials said.

The soldiers are from Mannheim and Stuttgart. The other servicemembers are two sailors from Naples, Italy; and airmen, from Spangdahlem Air Base, Germany, and from Incirlik Air Base, Turkey.

The six are in medical isolation at Landstuhl, living in temporary quarters in a building separate from the hospital. After visiting with them Monday morning, their attending physician reported they were improving, if not all better, Davis said.

"They’re doing well," he said, noting the patients have completed their five days of treatment on the anti-flu medication Tamiflu.

The six stricken military members had come into contact with each other while at Landstuhl, where they were receiving treatment for noncombat-related injuries.

While health officials in Europe continue to track the patients’ recent activity in an attempt to locate the source of the influenza A infection among the Landstuhl group, they also acknowledged that may not be possible.

"We might never know where it originated," said Dr. (Cmdr.) Timothy Halenkamp, occupational and environmental medicine specialist in Naples. "Sometimes, you don’t ever find the source."

Naples health officials are working with Landstuhl-based medical experts to try to pinpoint where one of the Naples sailors with "probable" H1N1 may have contracted the virus. The sailor reported the earliest onset of sickness among the group now in medical isolation.

Rapid tests done at the hospital in Naples of all those who had come in close contact with the sailor have proved negative for the influenza A strain of the virus, Halenkamp said.

"We just don’t know," Halenkamp said. "He could have gotten it on the plane up there; he could have gotten it while in Germany."

Hospital staff in Naples "remain vigilant" in screening all patients who report to the hospital complaining of flu-like symptoms, he added.

Likewise at Landstuhl, hospital patients and staff members who may have interacted with the six servicemembers have been briefed on good hygiene and cough etiquette, "which is the key to keeping this from spreading," Davis said.