"(Outbreaks are) often taking place within the community, and oftentimes we don't know that they're happening," Sarah R. Michaels, an assistant professor at Tulane University’s Celia Scott Weatherhead School of Public Health and Tropical Medicine, previously told USA TODAY. "Really, when we have these areas where people … are in really close contact, things like day care facilities, nursing homes and cruise ships, it’s more likely (to be) diagnosed, reported and brought to our attention."