Influenza (Flu)

Curious about other respiratory viruses?

Aside from influenza, there are other respiratory viruses that circulate throughout the year. See our Respiratory Viruses fact sheet for the similarities and differences between influenza, parainfluenza, adenovirus, respiratory syncytial virus (RSV), human metapneumovirus, rhinovirus, enterovirus, and coronavirus. If you have respiratory symptoms, talk to your health care provider about testing.


Summer Time Flu: Swine/Variant Influenza

The flu is an illness caused by the influenza viruses. Flu gets passed around every year, with some years being worse than others. While people may think about flu in the colder months, it can also spread in the summer.

Swine influenza is a respiratory disease of pigs caused by type A influenza viruses that regularly cause outbreaks of influenza in pigs. Influenza viruses that commonly circulate in swine are called “swine influenza viruses” or “swine flu viruses.”

Six pigs in a farm pen outside.

Humans can be infected with swine influenza viruses. When this happens, these viruses are called “variant viruses.” In Wisconsin, human infections caused by variant influenza are often associated with swine exhibitions at agricultural fairs. Visit Centers for Disease Control and Prevention's (CDC) website to take action to prevent the spread between pigs and people. If you're a fair organizer, or will be exhibiting pigs, review CDC's guidance.


This page has more general information on the flu, including information on signs and symptoms and resources.

This page has tips on ways to prevent the flu.


This page has information on influenza data and the Weekly Respiratory Report.

This page is for local health departments, health care providers, or those looking for information on reporting, surveillance, or diagnosis of the flu.


This page is for local health departments, health care providers, or those looking for resources for the flu education, outreach, vaccination logistics and quality improvement.

Questions about the flu? Talk to your doctor.
Or find answers to frequently asked questions and learn more about the flu with the Centers for Disease Control.

Last Revised: August 31, 2021