Thu September 11, 2003 06:34 PM ET By Paul Simao ATLANTA (Reuters) - The U.S. Army said on Thursday it did not know what had caused an outbreak of a severe type of pneumonia that killed two soldiers serving in Iraq and caused 17 on duty in the Middle East, Central Asia and the Horn of Africa to be hospitalized. The illnesses, which were reported in a study published by the Centers for Disease Control and Prevention, occurred between March and August in a group of full-time active duty personnel and reservists deployed in Iraq, Kuwait, Djibouti, Qatar and Uzbekistan....