SAN FRANCISCO, Dec. 8 — As the health officer of Alameda County, Dr. Anthony Iton is prepared to make tough choices if SARS re-emerges this winter or spring, as many infectious disease experts fear. The county, just across the bay from here, has identified two large buildings where, if voluntary steps to quell an epidemic were to fail, the authorities could sequester not just people who were sick but also people who might have been exposed to the SARS virus, Dr. Iton said. The buildings, he said, could house up to 100 people and could be guarded to keep anyone...