The Army is trying to figure out what is causing a rash of serious pneumonia (search) cases, including two fatalities, among troops serving in the Iraq war.

A six-person team of specialists was en route to Iraq on Friday to investigate 15 cases of pneumonia so serious that patients had to be put on ventilators to breathe and were evacuated from the region, the Army Surgeon General's (search) office said Friday.

Two soldiers died, 10 recovered and three remained hospitalized as of Friday, spokeswoman Lyn Kukral said. Most were in the Army, but at least one was a Marine.

The team on its way to Iraq includes infectious disease experts, laboratory officers and people who will take samples of soil, water and air.

So far, officials have identified no infectious agent common to all the cases. Officials said there was no evidence that any of the cases were caused by exposure to chemical or biological weapons, environmental toxins or SARS (search), severe acute respiratory syndrome, the disease first noted in China this year.

A two-person team already has gone to Landstuhl Regional Medical Center (search) in Germany, where most of the cases were treated after evacuation. The two teams also will review patient records and laboratory results and interview health care workers and patients, if possible, the Army surgeon general and U.S. Army Medical Command said a statement.

The teams will be looking for similarities among the cases, which so far have hit troops in geographically dispersed areas and from different units, said the Thursday statement. They also were spread over time, with three in March, three in April, two in May, three in June and four in July.

Most of the cases were in Iraq and occurred after the U.S.-led invasion began March 20, although some were among other troops deployed to the region in support of the campaign. Troops also were sent to Kuwait, Qatar, Saudi Arabia and other countries, but no breakdown was available on the number of cases outside Iraq, Kukral said.

Though only 15 cases were considered serious, about 100 cases have been diagnosed since March 1 among troops that began deploying late last year to the Persian Gulf area.

Armywide, pneumonia cases serious enough to warrant hospitalization happen in about 9 of 10,000 soldiers per year. Given the number of troops deployed, the 100 cases "do not exceed expectations," the surgeon general's office said.