"Influenza outbreak" refers to the widespread occurrence of the flu in a particular area or community. It means that many people in that place are getting sick with the flu at the same time. Full definition
This was the most severe influenza outbreak of the twentieth century and, in terms of total numbers of deaths, possibly the most devastating epidemic in human history. (religion-online.org)
Since 2003, there have been numerous reports of influenza outbreaks in veterinary hospitals, kennels, and shelters. (tampabayvets.net)
Public health officials already use several methods to track influenza outbreaks, but the data tends to be a week or two behind the actual epidemic. (health.com)