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1Acute respiratory illness (ARI)is non-specific syndrome that can be caused by infection with different respiratory pathogens that typically involves the airways within the nose and throat (i.e., the upper respiratory tract) and that may or may not include fever (measured by a thermometer) or feverishness (i.e., self-reported sense of fever). ARI is generally defined as the presence of two or more signs or symptoms such as fever, cough, runny nose or nasal congestion, or sore throat). ARI is a more sensitive (broader) syndrome than influenza-like illness (ILI) to describe illness consistent (although not specific) with influenza (flu) because fever or feverishness is not required. ARI can capture influenza virus infections without fever.
2Respiratory Activity is defined by: Minimal (0-10% of ED visits were for ARI), Low (10-15% of ED visits were for ARI), Moderate (15-20% of ED visits were for ARI), and High (20-25% of ED visits were for ARI), Very High (25% or more of ED visits were for ARI).
3According to CDC, the purpose of using broad acute respiratory illness (ARI) definition is "to assist state, tribal, local, territorial, and federal public health practitioners in identifying visits in the emergency department (ED) and urgent care (UC) settings with diagnostic codes associated with a broad range of acute respiratory illnesses. This includes codes associated with specific respiratory infections (e.g., Influenza, respiratory syncytial virus [RSV], or coronavirus), and codes associated with general respiratory illness such as cough or pneumonia. Co-circulation of multiple respiratory viruses has garnered interest in tracking the impacts of respiratory illnesses together. This is a new definition that was created to monitor the combined effects of multiple respiratory illnesses and aid in identification of the primary cause of increases through pathogen-specific surveillance. This aims for a broad view of respiratory visits and does not attempt to parse out visits due to a specific infection or condition. Additionally, historic baselines would exist and could be used to help determine if a new respiratory pathogen emerges." For additional information, please refer to https://knowledgerepository.syndromicsurveillance.org/sites/default/files/2023-08/CDC Broad Acute Respiratory DD v1 Factsheet.pdf
4The baseline for Emergency Department (ED) visits related to Acute Respiratory Illness (ARI) was calculated using the average percentage of visits during weeks with the lowest respiratory illness activity. This calculation was based on clinical and public health laboratory test positivity data from NREVSS for the three most recent respiratory illness seasons (2023–24, 2024–25, and 2025–26). Specimen data from HHS Region 5 was used as a reference for Kane County. The ARI-related ED visit baseline serves as a reference point for determining current levels of respiratory illness activity. For a detailed explanation of the baseline calculation, please visit: https://www.cdc.gov/respiratory-viruses/data/activity-levels.html#cdc_data_surveillance_section_7-data-notes.
5Rapid influenza testing cannot distinguish influenza infections caused by novel influenza A viruses. The sensitivity of this type of testing has been shown to range between 20-100% for seasonal influenza viruses. A negative result does not exclude influenza virus infection.
6The National Snapshot comes directly from the FluView interactive portal prepared by the CDC Influenza Division using ILINet data. FluView can be accessed at https://gis.cdc.gov/grasp/fluview/main.html.
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