Influenza Surveillance Report
Have questions? Here are answers to the most frequently asked questions about our data and methodology.
Frequently Asked Questions
Weekly flu report - details about the metrics
- 2023-2024 influenza season:
The 2023 – 2024 influenza season begins CDC Week 40 (week ending October 7, 2023) and ends CDC week 39 (week ending September 28, 2024). The Missouri Weekly Influenza Surveillance Report is updated each Friday from October 1, 2023 – May 18, 2024.
The Centers for Disease Control and Prevention
The Centers for Medicare & Medicaid Services
The Missouri Department of Health and Senior Services
The Electronic Surveillance System for the Early Notification of Community-based Epidemics, ESSENCE, is a software system that inputs electronic emergency department data for participating hospitals.
The United States Department of Health and Human Services
- Influenza Case
For this report, a case of influenza is equal to a laboratory confirmation of influenza. Laboratory-confirmed influenza is reportable in aggregate in Missouri (for more information see https://www.sos.mo.gov/cmsimages/adrules/csr/current/19csr/19c20-20.pdf) and includes positive results on any of the following test methods: rapid influenza diagnostic tests (antigen); reverse transcriptase polymerase chain reaction (RT-PCR) and other molecular assays; immunofluorescence antibody staining (Direct (DFA) or Indirect (IFA)); and viral culture.
Influenza-like illness. Defined as fever (temperature of 100°F [37.8°C] or greater) and a cough and/or a sore throat.
The U.S. Outpatient Influenza-like Illness Surveillance Network. ILINet consists of outpatient health care providers from around the country that report to CDC on a weekly basis.
The National Respiratory and Enteric Virus Surveillance System. NREVSS is a laboratory-based system that monitors temporal and geographic circulation patterns of various viruses. On a weekly basis, participating U.S. laboratories voluntarily report the total number of tests performed, the method used for detection, and the number of those tests with positive results.
The Missouri Health Surveillance Information System, a centralized and integrated database that allows the DHSS and local public health agency staff the ability to enter and update case report information, including aggregate reporting of laboratory-confirmed influenza cases.
The World Health Organization
- Outpatient Data
- ILI Activity Level
Data is sourced from ILINet. Levels of ILI activity are classified as minimal, low, moderate, high, and very high. Activity levels are based on the percent of outpatient visits due to ILI in a jurisdiction compared to the average percent of ILI visits that occur during weeks with little or no influenza virus circulation in that jurisdiction. For more information see https://gis.cdc.gov/grasp/fluview/main.html.
- Percent of Emergency (ED) Visits due to ILI
Data is sourced from the hospital emergency room visit chief complaint data reported through Missouri’s ESSENCE. ILI is defined by ESSENCE as Emergency Department chief complaints for Influenza or (Fever Plus and (Cough or Sore Throat) and not Non-ILI Fevers). The ESSENCE ILI Baseline is the mean percent of ILI visits for each week during the previous three influenza seasons when percentage of ILI visits were less than 2% of total visits, plus two standard deviations.
- ILI Activity Level
- Laboratory Data
- Weekly Percent Positivity
Data is sourced from NREVSS. The positivity rate is based on laboratory data submitted by participating clinical hospitals for the CDC week of report.
- Influenza A Subtype
Data is sourced from NREVSS. The data is based on which influenza A subtype had the highest proportion positive for the CDC week of report. Data may be limited on weeks with low influenza activity.
- Weekly Percent Positivity
- Case Data, Influenza Cases by Jurisdiction, and Influenza Cases by Week
Data is sourced from WebSurv. Influenza case data is entered by local public health agencies weekly.
- New Influenza Hospital Admissions by Week
Data is sourced from HHS Protect Hospitalization Surveillance. New hospital admissions are defined as patients who were admitted to an inpatient bed on the previous calendar day and had a positive influenza test at admission or during the 14 days prior. For more information see https://healthdata.gov/Hospital/COVID-19-Reported-Patient-Impact-and-Hospital-Capa/anag-cw7u and https://www.cdc.gov/flu/weekly/overview.htm#ILINet.
- Regional Data
Data is sourced from WebSurv. Rates are calculated using 2020 population data from the Missouri Information for Community Assessment (MICA), an interactive system that was developed to make health data accessible at the local level through an easy-to-use format. For more information see https://health.mo.gov/data/documentation/population/population-general-info.php and https://healthapps.dhss.mo.gov/MoPhims/MICAHome.
- Influenza Deaths
Data is sourced from Missouri’s death certificate data. Decedents with influenza listed as a cause or contributor to death are classified as an influenza-associated mortality. Death certificate data are generally available two weeks following the current CDC week. Death totals are cumulative from the start of the influenza season.
- Laboratory Data (Expanded View)
Data is sourced from ILINet. Laboratory surveillance data on influenza specimens from Missouri residents are reported by WHO/NREVSS collaborating laboratories. Data from both public health and clinical laboratories are included in the total number of respiratory specimens tested for influenza and the number positive for influenza viruses. ILINet laboratory data is generally available one week following the current CDC week. The 2020-2021 influenza season was unusually low due in part to the ongoing COVID-19 pandemic. Therefore, the influenza-associated data for the 2020-2021 influenza season are substantially different from previous seasons.