Mayo Clinic study provides insights into risk factors for severe COVID-19 in younger populations Using data from 9,859 COVID-19 infections, Mayo Clinic researchers have new insights into risk factors for younger populations, some of which differ significantly from their older counterparts. People younger than 45 had a greater than threefold increased risk of severe infection if they had cancer or heart disease, or blood, neurologic or endocrine disorders, the research found. These associations were weaker in older age groups. The study was published in Mayo Clinic Proceedings. The research team studied people living in a 27-county region of Southeast Minnesota and West Central Wisconsin surrounding Mayo Clinic in Rochester diagnosed with COVID-19 between March and September 2020. The study used the Rochester Epidemiology Project, a linkage of 1.7 million medical records from multiple health care systems that provides a full picture of risks for an entire geographical region.