Influenza Surveillance

2018 - 2019 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 40: Sept 30 - Oct 6, 2018 No Activity
Week 41: Oct 7 - Oct 13, 2018 No Activity
Week 42: Oct 14 - Oct 20, 2018 No Activity
Week 43: Oct 21 - Oct 27, 2018 Sporadic
Week 44: Oct 28 - Nov 3, 2018 Sporadic
Week 45: Nov 4 - Nov 10, 2018 Sporadic
Week 46: Nov 11 - Nov 17, 2018 Sporadic
Week 47: Nov 18 - Nov 24, 2018 Sporadic
Week 48: Nov 25 - Dec 1, 2018 Local
Week 49: Dec 2 - Dec 8, 2018 Local
Week 50: Dec 9 - Dec 15, 2018 Local
Week 51: Dec 16 - Dec 22, 2018 Regional
Week 52: Dec 23 - Dec 29, 2018 Regional
Week 1: Dec 30, 2018 - Jan 5, 2019 Regional
Week 2: Jan 6 - Jan 12, 2019 Regional
Week 3: Jan 13 - Jan 19, 2019 Regional
Week 4: Jan 20 - Jan 26, 2019 Widespread
Week 5: Jan 27 - Feb 2, 2019 Widespread
Week 6: Feb 3 - Feb 9, 2019 Widespread


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.