This dataset includes aggregated weekly influenza virus laboratory data that the Chicago Department of Public Health (CDPH) uses to monitor influenza activity and assess which influenza types and subtypes are circulating in Chicago. The data represent weekly positive influenza PCR tests voluntarily reported by network of several hospital laboratories in Chicago as well as two commercial laboratories serving Chicago facilities. The data includes positive test results by influenza type (influenza A and influenza B) as well as influenza A subtype (H3N2, H1N1pdm09) when available. These data do not include patient demographic or geographic information and represent both Chicago and non-Chicago residents tested by the reporting facility. Influenza laboratory data are available from the 2010-2011 season to present.

Two percentage fields are available in the dataset. Percentages are calculated for each characteristic group as follows:

The percentage of influenza types is calculated as the total number of positives tests for each influenza type divided by the total number of positive influenza tests reported (e.g., Influenza A/Influenza Positive). The percentage fields describe the percent of positive tests by influenza type each week (count_pct) and for the entire season to date (count_cum_pct).

The percentage of influenza A subtypes is calculated as the total number of positive tests for each influenza A subtype divided by the total number of positive influenza A tests reported (Influenza A Subtype/Influenza A). The percentage fields describe the percent of influenza A positive tests by subtype each week (count_pct) and for the entire season to date (count_cum_pct).

The percentage for characteristic group ‘Total Positive’ will always be 100% and does not represent influenza test positivity. For data on influenza test positivity see: https://data.cityofchicago.org/Health-Human-Services/Influenza-COVID-19-RSV-and-Other-Respiratory-Virus/qgdz-d5m4/about_data.

All data are provisional and subject to change. Information is updated as additional details are received. At any given time, this dataset reflects data currently known to CDPH. Numbers in this dataset may differ from other public sources.