Influenza (commonly called the flu) is a contagious respiratory illness caused by viruses. The flu usually comes on suddenly with symptoms including fever, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue. Most people who get influenza recover in several days to less than two weeks. Young children, older adults, pregnant women, and those with certain chronic medical conditions are at high risk of serious flu complications, possibly requiring hospitalization and sometimes resulting in death.

There are three types of influenza viruses: A, B and C. Influenza A and B cause seasonal epidemics almost every winter in the United States. Influenza C infections cause a mild respiratory illness and are not thought to cause epidemics.

While seasonal influenza viruses can be detected year-round in the United States, they are most common during the fall and winter. The exact timing and duration of flu seasons can vary, but activity often begins to increase in October. Most of the time flu activity peaks between December and March, and can last into May.

States report a variety of measures to the CDC for each week in the flu season (October to May) including:

Flu outbreaks can affect the operation of many organizations and a variety of decisions need to be made before and during the flu season to compensate for absenteeism and limit disease spread. Long-term care facilities and hospitals must determine if visiting policies should be modified. Health care providers need to schedule patients for vaccinations and obtain sufficient inventories of medications and supplies to treat flu sufferers. Schools experiencing severe outbreaks may choose to close. Local, state, and national public health organizations monitor flu activity and prepare awareness campaigns to encourage vaccination and proper hygiene. Advance planning decisions can be informed by an understanding of the year-to-year variation in flu activity, while decisions made during the flu season may benefit from monitoring weekly activity. In this case we will make use of Graph Builder to construct visualizations of flu activity on an annual and weekly basis for two states.