Complex sentence: Health officials 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.
Split into simpler sentences: Health officials 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.