Key points
U.S. virologic surveillance
Clinical Laboratories
Nationally, during Week 21, the percentage of respiratory specimens testing positive for influenza virus in clinical laboratories was 1.4%. The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| Week 21 | Data Cumulative since September 28, 2025 (Week 40) |
|
|---|---|---|
| No. of specimens tested | 30,574 | 2,577,927 |
| No. of positive specimens (%) | 427 (1.4%) | 320,794 (12.4%) |
| Positive specimens by type | ||
| Influenza A | 94 (22.0%) | 226,359 (70.6%) |
| Influenza B | 333 (78.0%) | 94,435 (29.4%) |
Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza virus type/subtype/lineage. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
| Week 21 | Data Cumulative since September 28, 2025 (Week 40) |
|
|---|---|---|
| No. of specimens tested | 299 | 99,396 |
| No. of positive specimens | 41 | 65,615 |
| Positive specimens by type/subtype | ||
| Influenza A | 15 (36.6%) | 55,327 (84.3%) |
| Subtyping Performed | 12 (80.0%) | 45,551 (82.3%) |
| (H1N1)pdm09 | 4 (33.3%) | 6,168 (13.5%) |
| H3N2 | 8 (66.7%) | 39,381 (86.5%) |
| H3N2v† | 0 | 0 |
| H5* | 0 | 2 (<0.01%) |
| Subtyping not performed | 3 (20.0%) | 9,776 (17.7%) |
| Influenza B | 26 (63.4%) | 10,288 (15.7%) |
| Lineage testing performed | 12 (46.2%) | 4,213 (41.0%) |
| Yamagata lineage | 0 | 0 |
| Victoria lineage | 12 (100%) | 4,213 (100%) |
| Lineage not performed | 14 (53.8%) | 6,075 (59.0%) |
Novel Influenza A Virus Infections
No new confirmed human infections with avian influenza A(H5) virus were reported to CDC this week. To date, person-to-person transmission of avian influenza A(H5) virus (H5 bird flu) has not been identified in the United States.
The CSTE position statement, which includes updated case definitions for confirmed, probable, and suspected cases, is available at http://www.cste.org/resource/resmgr/position_statements_files_2023/24-ID-09_Novel_Influenza_A.pdf.
An up-to-date A(H5) human case summary during the current outbreak by state and exposure source is available at www.cdc.gov/bird-flu/situation-summary/index.html.
Information about avian influenza is available at https://www.cdc.gov/flu/avianflu/index.htm. A(H5N1) virus interim recommendations for Prevention, Monitoring, and Public Health Investigations are available at https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html.
Outpatient and Emergency Department Illness Surveillance
Outpatient Respiratory Illness Visits
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and may capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity.
Nationwide during Week 21, 1.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
Outpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
During Week 21, the percentage of visits for respiratory illness reported in ILINet was 5.2% among those 0-4 years, 2.2% among those 5-24 years, 1.3% among those 25-49 years, 0.9% among those 50-64 years, and 0.7% among those 65 years and older.
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Activity Level | Number of Jurisdictions | Number of CBSAs | ||
|---|---|---|---|---|
| Week 21 (Week ending May 30, 2026) |
Week 20 (Week ending May 23, 2026) |
Week 21 (Week ending May 30, 2026) |
Week 20 (Week ending May 23, 2026) |
|
| Very High | 0 | 0 | 0 | 0 |
| High | 0 | 0 | 0 | 0 |
| Moderate | 0 | 0 | 0 | 0 |
| Low | 0 | 0 | 13 | 6 |
| Minimal | 55 | 55 | 692 | 696 |
| Insufficient Data | 0 | 0 | 224 | 227 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
National Syndromic Surveillance System (NSSP)
The overall percentage of emergency department (ED) visits with a discharge diagnosis of influenza reported in NSSP was 0.2% during Week 21. The percentage of visits was 0.4% among those 0-4 years, 0.6% among those 5-17 years, 0.2% among those 18-64 years, and 0.1% among those 65 years and older.
Hospitalization surveillance
FluSurv-Net
Influenza-Associated Hospitalizations: The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 10% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 30,454 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2025, and May 30, 2026. The weekly hospitalization rate observed during Week 21 was 0.1 per 100,000 population. The cumulative hospitalization rate observed in Week 21 was 87.4 per 100,000 population.
Additional FluSurv-NET data are available on FluView Interactive including hospitalization rates for the current and past seasons by age, sex, and race/ethnicity (http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html) as well as data on patient characteristics at: (http://gis.cdc.gov/grasp/fluview/FluHospChars.html.)
FluSurv-NET data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at Estimated US Flu Disease Burden | Flu Burden | CDC.
**In this figure, weekly rates for all seasons prior to the 2025-26 season reflect end-of-season rates. For the 2025-26 season, rates for recent hospital admissions are subject to reporting delays and are shown as a dashed line for the current season. As hospitalization data are received each week, prior case counts and rates are updated accordingly.
National Healthcare Safety Network (NHSN) Hospital Respiratory Data
Hospitals report to NHSN the weekly number of patients with laboratory-confirmed influenza who were admitted to the hospital. Nationally, during Week 21, 997 (0.3 per 100,000 population) laboratory-confirmed influenza-associated hospitalizations were reported. When examining rates by age, the highest hospital admission rate per 100,000 population was among those 65+ years (0.8), followed by 0-4 years (0.5), and 50-64 years age group (0.2).
National Healthcare Safety Network (NHSN) Long-Term Care Respiratory Pathogens & Vaccination Module
Long-term care facilities (LTCFs [e.g., Nursing homes/skilled nursing facilities]) report respiratory pathogen (e.g., COVID-19, influenza, and RSV) data, including vaccination, cases, and hospitalizations among residents, to the NHSN Long-Term Care Respiratory Pathogens & Vaccination Module.
NHSN long-term care influenza hospitalization data are not included in summer FluView reports.
Mortality surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
The NCHS mortality surveillance data were not available for inclusion in this week's report. The following graph includes data through Week 20 of 2026 (the week ending May 23, 2026) and will be updated when data are available.
Influenza-Associated Pediatric Mortality
Five influenza-associated pediatric deaths occurring during the 2025-2026 season were reported to CDC during Week 21. The deaths occurred during weeks 51, 4, 8, 19 and 20 (the weeks ending December 20, 2025, January 31, 2026, February 28, 2026, May 16, 2026, and May 23, 2026). A total of 179 influenza-associated pediatric deaths occurring during the 2025-2026 season have been reported to CDC.
All data in this report are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Additional National and International Influenza Surveillance Information
Additional surveillance information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada's weekly FluWatch report.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.