Influenza Surveillance

2019 - 2020 Flu Activity Report

While influenza is not a reportable disease in Illinois, IDPH examines reports from many health care sites throughout the state. These sites include physician offices, emergency departments, and other clinics that report acute illness with influenza-like illness, and institutional settings such as nursing homes and prisons that report outbreaks. Accordingly, IDPH monitors disease trends and influenza activities as they occur on a weekly basis.

A detailed surveillance report for each week can be viewed by clicking on the desired week in the table below. This weekly surveillance report summarizes regional and state influenza data used to determine the weekly influenza activity level and national activity levels reported by state and territorial epidemiologists.

Report Activity Level
Week 2: January 5, 2020 - January 11, 2020 Widespread
Week 1: December 29, 2019 - January 4, 2020 Widespread
Week 52: December 22, 2019 - December 28, 2019 Widespread
Week 51: December 15, 2019 - December 21, 2019 Widespread
Week 50: December 8, 2019 - December 14, 2019 Regional
Week 49: December 1, 2019 - December 7, 2019 Regional
Week 48: November 24, 2019 - November 30, 2019 Local
Week 47: November 17, 2019 - November 23, 2019 Local
Week 46: November 10, 2109 - November 16, 2019 Local
Week 45: November 3, 2019 - November 9, 2019 Local
Week 44: October 27, 2019 - November 2, 2019 Local
Week 43: October 20, 2019 - October 26, 2019 Sporadic
Week 42: October 13, 2019 - October 19, 2019 Sporadic
Week 41: October 6, 2019 - October 12, 2019 Sporadic
Week 40: September 29 - October 5, 2019 No Activity


No Activity No lab confirmed cases †
Sporadic Activity Isolated lab-confirmed cases OR Lab confirmed outbreak in one institution ‡
Local Activity
Recent (within the past 3 weeks) lab evidence of influenza in region with increased ILI* OR Recent (within the past 3 weeks) lab evidence of influenza in region with the outbreaks; virus activity is no greater than sporadic in other regions**
Regional Activity Increased ILI* in >2 but less than half of the regions AND recent (within the past 3 weeks) lab confirmed influenza in the affected regions. OR Institutional outbreaks (ILI or lab confirmed) in >2 and less than half of the regions ANDrecent lab confirmed influenza in the affected regions**. A region is defined as the regions States use for public health purposes.
Widespread Activity Increased ILI* and/or institutional outbreaks (ILI* or lab confirmed) in at least half of the regions** AND recent (within the past 3 weeks) lab confirmed influenza in the state.


*ILI activity can be assessed using a variety of data sources including sentinel providers, school/workplace absenteeism, and other syndromic surveillance systems that monitor influenza-like illness.

† Lab confirmed case=case confirmed by rapid diagnostic test, antigen detection, culture, or PCR. Care should be given when relying on results of point of care rapid diagnostic test kits during times when influenza is not circulating widely. The sensitivity and specificity of these tests vary and the predicative value positive may be low outside the time of peak influenza activity. Therefore, a state may wish to obtain laboratory confirmation of influenza by testing methods other than point of care rapid tests for reporting the first laboratory confirmed case of influenza of the season.

‡ Institution includes nursing home, hospital, prison, school, etc.

** Region: population under surveillance in a defined geographical subdivision of a state. A region could be comprised of 1 or more counties and would be based on each state's specific circumstances. Depending on the size of the state, the number of regions could range from 2 to approximately 12. The definition of regions would be left to the state but existing state health districts could be used in many states. Allowing states to define regions would avoid somewhat arbitrary county lines and allow states to make divisions that make sense based on geographic population clusters. Focusing on regions larger than counties would also improve the likelihood that data needed for estimating activity would be available.