Influenza:
Tracking Influenza in Wisconsin

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Influenza Surveillance
Annual Report 2007-2008 (PDF, 347 KB)
Weekly Report Description (PDF, 32 KB)
2012 Surveillance Report - Week 4 (PDF, 302 KB)

Influenza-Associated Hospitalizations
Surveillance Letter
Clarification Letter
EpiNet Surveillance Definitions

On this page
How do you keep track of influenza in Wisconsin?
Do all cases of influenza in the state get reported?
Why aren't there more confirmed cases of influenza?

How do you keep track of influenza in Wisconsin?

Wisconsin monitors influenza activity in several ways:

• Voluntary submission of isolates by clinical virology laboratories to the Wisconsin State Laboratory of Hygiene (exit DHS).
• Voluntary reporting by virology laboratories that participate in the Wisconsin Laboratory Information Network (LIN) of positive test results and total number of respiratory virus specimens tested.
• Voluntary reporting by a statewide network of sentinel clinicians of the number of patients presenting with influenza-like illness (ILI) and the total number of patient visits by age group each week.  This reporting occurs year-round.
• Voluntary reporting of influenza outbreaks in long-term care facilities, schools and other congregate settings.

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Do all cases of influenza in the state get reported?

No – many cases are never reported because influenza is not a reportable disease in Wisconsin. We do not attempt to track – or get reports on – all cases. Most cases are never reported to anyone, since most people with influenza never see a doctor about their illness – and many of those who do are never tested.

Even if it were possible to track all cases of influenza in the state, it wouldn’t be useful to do so. Influenza is so common during the winter months that we could never actively investigate all of the cases reported to us. We would simply be “counting cases” – and that wouldn’t help us protect the health of the public.  Because some providers actively test for influenza and others do not, counting the number of cases would not be a reliable way to track influenza.

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Why aren't there more confirmed cases of influenza?

Although confirmed cases may provide a rough indication of activity, that's not the primary reason we keep track of them.  Confirmed cases allow us to: 

(1) determine when we first started to see influenza activity each year (the "first influenza case of the season"); and 

(2) determine what strains of influenza are circulating in any given year.

That's the main reason we confirm cases in the lab- finding out what kind of influenza is around, and whether the current vaccine protects against it.  Only a tiny fraction of all cases are ever confirmed in our lab.

 For seasonal influenza information in your community,
contact local health department or
Thomas Haupt
   Influenza Coordinator
  WI Division of Public Health
  Bureau of Communicable Diseases & Emergency Response
     608-266-5326 - Phone 
     608-261-4976 - Fax

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Last Revised: February 06, 2012