Coronavirus cases are climbing rapidly among young adults in a number of states where bars, stores and restaurants have reopened — a disturbing generational shift that not only puts them in greater peril than many realize but poses an even bigger danger to older people who cross their paths. In Oxford, Mississippi, summer fraternity parties sparked outbreaks. In Oklahoma City, church activities, fitness classes, weddings and funerals seeded infections among people in their 20s, 30s and 40s. In Iowa college towns, surges followed the reopening of bars. A cluster of hangouts near Louisiana State University led to at least 100 customers and employees testing positive. In East Lansing, Michigan, an outbreak tied to a brew pub spread to 34 people ages 18 to 23.