(Click here for a graphic explaining the types and causes of pneumpnia.)

ARLINGTON, Va. — A definitive cause of the debilitating cases of pneumonia plaguing troops deployed to the U.S. Central Command continues to elude Pentagon health officials, though physicians have established a link between two cases.

Of the 15 troops who have suffered serious bouts in recent months, two have tested positive for a bacterium; the only connection so far, officials said Tuesday during a Pentagon briefing.

In those two cases, physicians identified streptococcus pneumonia, the most common cause of bacterial pneumonia. According to the Centers for Disease Control and Prevention, it is the only form for which a vaccine is available.

Two other troops among the 15 acute cases have died, and though the cause of death has not been named officially, tests have shown no bacteria were present, said Col. Robert DeFraites, chief of preventative medicine for the Army Surgeon General’s office.

DeFraites said the cases are not from any chemical or biological attacks. “We have found no evidence of anthrax, smallpox or any biological or chemical agents,” he said.

Pneumonia is an infection or inflammation of lungs in which air sacs fill with liquid and prevent oxygen from reaching the body’s blood supply. There are two basic types: those caused by infections such as bacteria, fungi and parasites; and the noninfectious caused by elements such as dust, metals, smoke and pollution.

Of the 15 serious cases, two were logged in March, two in April, one in May, six in June and four in July. The earliest cases were among troops in Kuwait. Fourteen are soldiers and one is a Marine. Fourteen are men and one is a woman.

None of those diagnosed have been from the same units, and none have spread the illness through human contact, DeFraites said. According to the CDC, transmission of streptococcus pneumonia is person-to-person.

Since March, the Army has seen about 100 pneumonia cases throughout the CENTCOM region, a number that does not surprise the Army medical community given that roughly 250,000 troops have been deployed, DeFraites said.

“[The number] is about the amount one might expect in a population of troops deployed based on our background information and experience,” he said.

Each year, the Army sees about 400 to 500 cases of pneumonia worldwide. Between 1998 and 2002, 17 soldiers worldwide have died of pneumonia or complications of pneumonia.

“The other interesting thing about these 15 cases … is that they have occurred all throughout the Southwest Asia region,” he said. Cases have popped up as far north as Uzbekistan and south as Qatar. Ten of the 15 serious incidents have occurred in Iraq.

Officials are not providing details about the two soldiers who died other than to say one died in June and one in July. Both fatal cases originated in Iraq.

Generally, symptoms of pneumonia can include chills, sweating, chest pain, cough, fever and altered mental status.

Troops in the region are being told to keep themselves well hydrated, to guard against ingesting dust and to refrain from smoking, which exacerbates the potential of developing problems.

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