The state Division of Public Health said Saturday that at least three teens staying at a rental unit in Dewey Beach tested positive. More than a dozen teens were staying there at the time.
The health department says the teens also attended large parties in nearby Rehoboth that may have exposed more than 100 partygoers to the virus.
Health officials did not specify the time of their stay.
They say they are trying to trace the infected teens' potential contacts.