Lt. Col. Janice M. Rusnak, recently arrived at the U.S. military hospital in Landstuhl, Germany, for a tour as infectious-diseases specialist, walked into the third-floor intensive care unit. She didn't know the name of the patient she wanted to see. But she had what she considered a fairly good description. Can you point me to the soldier from Iraq who's on a ventilator? she asked a nurse. The one with acute respiratory distress syndrome.What's clear so far is this: Since early March, about 100 soldiers deployed to the Persian Gulf region and Central Asia have contracted pneumonia. About 30 have...