Influenza Surveillance

2016 - 2017 Flu Activity Report

While influenza is not a reportable disease in Illinois, the Illinois Department of Public Health examines reports from many health care sites throughout the state. These sites include physician offices, emergency departments and nursing homes that report acute illness, and schools that report absenteeism rates. Accordingly, the Department 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 11: March 12 - March 18, 2017 Regional
Week 10: March 5 - March 11, 2017 Regional
Week 9: Feb 26 - March 4, 2017 Regional
Week 8: Feb 19 - Feb 25, 2017 Widespread
Week 7: Feb 12 - Feb 18, 2017 Widespread
Week 6: Feb 5 - Feb 11, 2017 Widespread
Week 5: Jan 29 - Feb 4, 2017 Widespread
Week 4: Jan 22 - Jan 28, 2017 Widespread
Week 3: Jan 15 - Jan 21, 2017 Widespread
Week 2: Jan 8 - Jan 14, 2017 Widespread
Week 1: Jan 1 - Jan 7, 2017 Localized
Week 52: Dec 25 - Dec 31, 2016 Localized
Week 51: Dec 18 - Dec 24, 2016 Localized
Week 50: Dec 10 - Dec 17, 2016 Sporadic
Week 49: Dec 4 - Dec 10, 2016 Sporadic
Week 48: Nov 27 - Dec 3, 2016 Sporadic
Week 47: Nov 20 - Nov 26, 2016 Sporadic
Week 46: Nov 13 - Nov 19, 2016 Sporadic
Week 45: Nov 6 - Nov 12, 2016 Sporadic
Week 44: Oct 30 - Nov 5, 2016 No Activity
Week 43: Oct 23 - Oct 29, 2016 No Activity
Week 42: Oct 16 - Oct 22, 2016 No Activity
Week 41: Oct 9 - Oct 15, 2016 No Activity
Week 40: Oct 2 - Oct 8, 2016 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.