Complex sentence: Health officials later monitored 50 low-and 10 high-risk contacts, the high-risk contacts being Duncan's close family members and three ambulance workers who took him to the hospital.
Split into simpler sentences: Health officials later monitored 50 low-risk contacts, and 10 high-risk contacts. The 10 high-risk contacts are Duncan's close family members and three ambulance workers who took him to the hospital.